HIGH ISO AND VIDEO
In terms of high ISO performance and video, the two cameras perform pretty much as expected. The Fuji is better at keeping noise down in low light situations, though all m4/3 cameras have improved in this area and Olympus have now decided to take video seriously and the OM-D E-M5 II has the capacity to produce pretty decent footage. The Fuji? Well video is as poor as ever with the X-T1. Low bitrate and artefacts contribute to a pretty poor effort. The only good thing about Fuji video is they offer it.
Olympus raw files work very well in Photoshop / Lightroom, whereas Fuji have far too much background noise reduction in their own and Adobe's software for my taste. Though programmes like Iridient Developer and Photo Ninja do a better job with Fuji raw files, with the proviso that they generate more noise.
Much of the above has been dealt with in some depth via these links:-
There are however two things that the OM-D E-M5 II has that the Fuji doesn't and they are worthy of mention. The 5-Axis in body stabilisation and the 64MP raw / 40 MP jpg. high resolution mode. Both are only in the Olympus, there are no X-Ti equivalents as Fuji have chosen to go the lens stabilisation route. As I've written in previous posts, I'm very impressed by the Olympus IBIS. For me it's not essential and is most useful in terms of allowing me to create smooth hand held video, but it is there and it works very well.
To a certain extent the other Olympus 'extra' the high-res mode which creates 40MP jpgs. or 64 raw files is also dependent on subject matter not moving about, in fact it has to be completely still or else all sorts of artefacts appear in the images. But if still life / studio work is your forte, then this is a very useful option.
In other comparisons, the Olympus AF is faster, allowing images to be captured more efficiently, the Fuji has a slightly better and larger image viewfinder and the focus peaking and manual focusing option is also much quicker and easier than with the Olympus which is far too fiddly. Both have the option of electronic silent shutters and both also have the option of battery grips, which is essential for any situation that will yield a lot of images since both cameras have poor shots per battery ratios.
THE f/2.8 PRO SPEC. LENSES.
It's good to see MCE (Mirrorless / CSC / E.V.I.L) cameras coming up with what are regarded as professional specification zooms. While neither has disappointed me in terms of performance, it's almost impossible for me to give an assessment of how they compare, without taking account of how they interact with their respective cameras, sensor and the choices the manufacturers make concerning how the jpgs. and raw files are processed. The results each produce is very much part of a package. Having said that, I haven't been disappointed with the results from either. Both are decent at f/2.8, both have acceptably sharp edges and corners and neither exhibits significant CA and fringing problems. In fact they are amongst the very best that their respective lens ranges can offer. And that is, after all, exactly how it should be.
Lenses such as these have often been thought of as tools for wedding, event, news and even studio photographers. But they are equally at home for all kinds of general use. In fact having that fast f/2.8 aperture at the end of each zoom is pretty useful under most circumstances and allows sharp images at lower ISO's with faster shutter speeds. And the respective packages do the job that they were intended for very well indeed.
The Fuji 16-55mm f/2.8 is a pretty chunky best however. It's 655g compared to the 382g of the Olympus and significantly bigger. Personally I like the feel of it, but if you are planning to carry one of these around all day, it's worth being aware of that. Incidentally, the 'full-frame' Nikon 24-70mm f/2.8 is 900g, but the Canon 24-70mm f/2.8, again full-frame, is only 805g, which shows the APS-C sensor covering Fuji to be a bit of a beast since it's only 150g lighter for just over half the coveragec.
Now which one you might choose depends to a large extent on what system you're using currently. There is no suggestion that one lens is streets ahead of the other in terms of performance, so system changing performance doesn't occur. Plus it is worth pointing out that m4/3 users have an alternative with the Panasonic 12-35mm f/2.8 with built-in image stabilisation, so if you have a Panasonic m4/3 camera, that may well prove to be the more attractive alternative.
HOW ARE THE CAMERA AND LENS FOR PROFESSIONAL USE?
Are either of these combinations an option in terms of professional use? Well the answer is obviously yes, since there are many pro. photographers who use them for their work. Or more accurately, they say they do or have used them on occasions. Now I'm as keen on small light cameras as the next photographer, but there are certainly issues that both combinations have. The first is that both both camera / lens outfits require extra batteries for any situation that is going to produce a lot of images. This means there will probably be missed shots, since neither camera has an accurate battery meter. Both cameras also struggle with with speed of capture. Sure the Olympus has pretty nippy AF, but the standard shutter open, shutter closes, shutter opens, closes and opens again routine that occurs for every shot does mean instant picture grabbing is harder to accomplish. Both cameras are still only 16MP, while DSLR's operate in the 22-36MP range these days, even with the budget / enthusiast APS-C sensor models. And there are many photographers, including myself, who still prefer optical viewfinders.
HOW ARE THE CAMERA AND LENS FOR ENTHUSIAST USE?
This is slightly different and personally for the majority of my photographic work I would be looking at camera performance in this band, since I'm not usually working in a stressful, time consuming, 'have to get the shot' situation any more. And in fact both camera / lens combinations would work very well for weddings for example, since these are generally slow paced, predictable and a picture taking scenario where the photographer does have an element of control. And this capability extends to the majority of photographic scenarios most of us will be involved in, most of the time. And unless you are involved in sports, news and any other kind of fast-moving action photography, then both camera / lens combinations would serve you very well.
THE f/2.8 LENSES VERSUS FAST PRIMES
While zooms of this nature are often thought of as being useful in most situations, there is an view that they aren't wide enough, they aren't long enough and they aren't fast enough. Certainly, when I was shooting weddings and indoors events I never used one. I always used fast primes, usually having something like a 28 or 35mm f/1.8 on one camera and an 85mm f/1.8 on another. I even had a couple of f/1.2 lenses, though would only ever use those wide open in 'emergency' situations. So, in terms of personal preference and the way I work, I haven't gone for that f/2.8 standard zoom for pressured pro. work. However for my general landscape and travel work I've found both the Olympus and Fuji lenses to be very useful indeed. But again given the choice between the Olympus 12-40mm f/2.8 lens and the soon to be available 7-14mm f/2.8 option, I would probably go for the wider choice. And in fact, if that choice does exist, then a wide fast zoom and a telephoto zoom is often the preference of other professionals that I know. I did meet a wedding photographer who uses two Nikon D4's and 14-24mm f/2.8, 24-70m f/2.8 and 70-200mm f/2.8 lenses (or again says he does!!) but if indeed he does carry that lot around, then he's welcome to it!
And that of course is the advantage of these 'pro-spec' f/2.8 systems. That they are smaller, lighter and cheaper alternatives to the 'full-frame' DSLR workhorses that many professionals and serious enthusiasts use. And for general everyday photography they work just fine. Constant lens changing is a pain, so anything that reduces that to a minimum is useful.
BOTTOM LINE - WHICH DO I PREFER?
This isn't easy. The OLYMPUS OM-D E-M5 II 12-40mm f/2.8 combination would seem to have advantages over the Fuji in all but low light / high(er) ISO performance, but I always liked the FUJI X-T1 16-55mm f/2.8 in terms of handling and I have no problem with that big camera feel. But then perhaps the clue is in the fact that I used the word liked. As that indicates I don't have the Fuji camera or lens any more, I've recently sold the last remnants of what was at one time an extensive Fuji outfit. Whereas I still have the Olympus. So it seems I've made my choice.
However it's not quite as simple as that. For my kind of scenic, location work, the Olympus camera lens duo, with it's extra sharpness at low ISO's and the possibility of quick workflow via Photoshop is a big advantage. To get the look I want, the results from my Olympus outfit takes less time for me than the results from the equivalent Fuji outfit. And the fact that I've started shooting a lot of stock video clips has meant that any current Fuji X camera is pretty much out of the question. And that is indeed the main reason for my moving away from Fuji as my primary MSE camera system. Fuji video just isn't good enough for me and for all the handling and aesthetic charms of my Fuji X cameras, there is no point in my having lots of money invested in a set of cameras and lenses that don't produce acceptable video I can sell (or try to!).
And so of the two, I would conclude that the Olympus is a better hybrid option for me. But then if I was shooting a lot indoors and not interested in video I'd probably have chosen the Fuji.
These two camera lens combinations can be seen as pretty decent pro-spec options for photographers looking for general all-round picture taking capabilities. Neither will pass the work optimally and speedily under all circumstances, in all situations, test and that is still the territory occupied by top of the range DSLR's and lenses. But they are very definitely getting there. And to be honest, they have certainly 'done the business' for me. Whether or not they are what you want, only you can answer, but from my experience both Olympus and Fuji have come up with high quality options that won't break the bank or your back. (Though the Fuji might give your back a bit of a testing!) Ultimately, it's our abilities as photographers rather than the gear we use that determines the quality of our output, but owning and using decent gear can only be an advantage. And decent gear is what this is. Not the best I've used, but certainly in the ball park and with only a few reservations that I've dealt with in the many articles I've written about all of this.
If you've already chosen Fuji or Olympus then you're probably happy with what you've got and neither camera or lens has compelling reasons to make people change systems, as far as I'm concerned. However, some thought as to what might be the common photographic situations that you find yourself in, would be useful if you are considering one or other of these choices, if you are looking for a new system. But finally I have to say I've produced many images I'm pleased with using both and at the end of the day that's what really important.