In that regard, I have made the Epson look sharper than this Viewsonic for some comparisons, but if I play with the Viewsonic in the same fashion, utilizing more than standard amounts of sharpness and other related controls, I can almost certainly make you believe it is sharper than the $5K true 4K Sony, which in turn will not be hard looking, and be more natural. - Once again, there are always trade-offs. (And you can crank up the controls on the Sony...)
In the image player above, there are a number of photos of 4K images, and then closeups of one small section (so you can really see "sharpness"). In addition, we have provided the same close-up image from some other 4K capable projectors for quick comparison. The close-up of credits from Ghostbusters (the lab image), and the close-up of the Bigalow space station from Journey to space, make for some interesting viewing. With other projectors from the non 4K UHD Epson 5040UB up to shots from true 4K Sonys, you get to appreciate the slight differences.
For these two sets (Space - Bigalow, and Ghostbusters 2016 Lab credits) there's an interesting mix. Following the Viewsonic enlarged image, for the Bigalow space station, is the Epson 5040UB, then the Acer VL7860 (higher res 4K UHD panels - and a laser engine), and the $7999 Sony VW385ES pure 4K projector, for your consideration. The same sequence follow in order for the Lab credits from Ghostbusters, with the addition of two more images. The second last in the sequence is the higher end BenQ HT9050 - a 4K UHD projector (larger DLP chips), and superior optics. you can see the difference a serious lens makes. Finally, is the HT2550 at the end, virtually indistinguishable from the Viewsonic!
Bottom line on the PX727-4K Projector's Sharpness: It's as sharp as one would expect. On true 4K content it easily looks sharper than any normal 1080p projector working with 1080p content. That is the goal after all. You get step up sharpness and detail performance compared to 1080p non-pixel shifters. Spend more and you can have the same tech, or have higher native resolution, with better, and more expensive optics, than the PX727-4K projector, and you will, upon inspection see even sharper images.