First things first: you close with
How good do the pictures look on them? (Cause that’s what matters…).
Both of these cameras are capable of amazing, grade A+++, top-notch, award-winning, superlative images. This is in fact true of any mainstream brand-name largish-sensor camera today — review sites that try to tell you otherwise do so largely because they’d have no readership if they didn’t stress important crucial differences to agonize over.
My advice to you is to stop agonizing and pick one. You’ve got the basic differences down. I’ve used the Fujifilm X-T10 (as well as the X-T2) , and the Pentax K-5II (and many of its predecessors) extensively, and I can very confidently say that you can be extremely happy with either.
You’ve got the differences down pretty well. There are two more worth mentioning, both in the Pentax column.
First: in-body image stabilization with Pentax, which can be quite a boon especially with Pentax’s lovely prime lens lineup. You’ve spec’d out the Pentax with an 18-135 lens — if you switch to the 18-135mm Fujifilm lens, you get OIS, but raise your initial cost by a full 50%, and there’s just no way to get OIS in a portrait prime. So, there is that to consider.
Second: battery life. This is an inherent disadvantage of mirrorless (since the sensor and an LCD screen need to be active much more often), and Fujifilm has chosen a rather small capacity battery. This isn’t crippling, but I’d recommend at least one spare battery for a Pentax setup and three or four spares for Fujifilm.
All in all, I understand the problem deciding, because there isn’t a clear single winner when you add everything up — but again, that’s because both are winners. As full disclosure, I switched from Pentax to Fujifilm myself, but if someone waved a magic wand at me and compelled me to switch back, I wouldn’t be devastated or anything. They’re both great systems.
If you’re really not leaning one way or another, and won’t be satisfied taking a coin flip, one option is to rent each for a couple of weeks to really get a feel for each. (I recommend two weeks rather than one, because otherwise you’ll be caught in first impressions, which sometimes differ from familiar use.) LensRentals.com is basically the industry gold standard here (not affiliated, just a happy occasional customer), and you can rent the either setup (including a charger and an extra battery for Pentax and two extra for Fujifilm) for about $250. That’s not an insignificant outlay, but if you’re worried about having “grass is greener” regrets after your purchase, it might be worth it.
The one final bit of advice I’d give is that to get the most from either, you really will want to move on from the kit-style zoom lenses. Both systems have beautiful prime lenses that, really to me, are key reasons to pick these over other systems. In fact, personally, I’d suggest skipping the zooms entirely and starting with, say:
Pentax DA 21mm f/3.2 AL Limited + DA 50mm f/1.8 + DA 70mm f/2.4 Limited
Fujifilm XF 23mm f/2 R WR + XF 50mm f/2 R WR + maybe (see note below) XF 80mm f/2.8 R LM OIS WR Macro
— or even stretching for one the fancier primes in the system you choose. You’ll almost certainly grow beyond the kit zooms you’re looking at now, but these lenses you’ll be happy to keep forever.
The 21/23mm lenses will give you a field of view similar to what is typical of cell phones, and then you have the other lenses when you want to “zoom in” for more close-up detail. (Unfortunately, Fujifilm does not currently have anything like Pentax’s 70mm or 77mm lens — it’s kind of a gap in the lineup from my point of view; there’s a nice 80mm but it’s large and expensive.) This advice may seem a bit limiting, but in practice it’s not really important to have smooth coverage of every focal length, so a setup like this can be just as versatile and you get faster aperture and lighter smaller lenses with higher optical quality for the price level. And it’s not just me with this kind of recommendation — see the (in)famous “Letter to George” article from Michael Johnston.
But even with this advice, the real last word is the same as the first: stop worrying and, as the metaphor goes, pull the trigger (or, perhaps we should say, click the shutter). Pentax or Fujifilm, zoom or prime, it’s all great and the better thing is to get started.