As a general rule these 4K UHD projectors will have a native sharpness advantage over the one step down 1080p pixel shifters, and also a general rule is that 4K UHD isn't going to resolve as much detail/sharpness as true 4K. After that, it's up to the implementations of the various manufacturers.
Of course all of these projectors offer some sort of sharpening/detail enhancement, which like other forms of processing comes with some trade-offs.
The better the image processing the more sharpening and detail enhancement you can get, before other, undesirable, artifacts become visible. Our "cautionary tale" would be Epson's 5040UB. It is lower native resolution being a 1080p pixel shifter, but they offer extensive, and very good image processing when it comes to sharpness. Still, while the 5040UB, say at Image 4, can look as sharp as these 4K UHD projectors, there is some trade-off, which I often describe as being sometimes most noticeable on close ups of faces.
I do use Image Enhancement 4 sometimes, but mostly limit that control to 2, which easily eliminates most of the hardness, but still appears crisper than not using the control at all, or even the 1 setting. This, folks, is what it's all about - trade-offs. Still, with the Epson using settings of 2 or less, compared to the Optoma UHD60 or 65, the Optomas are definitely noticeably, if only slightly, sharper than the Epson! Clear?