The only USP I have is a .40 police trade-in that I got a good deal on. I put a factory threaded barrel in it because suppressed is always better. It's a great pistol however I think the HK45 is the logical evolution of the USP.
While my Octane .45 was in NFA jail I looked at different hosts and ended up with the HK45CT. I have pretty big hands and shot a friends HK45 fullsize and loved it, however even with the 8 round mags on the compact I am able to get a full grip. It also came with a threaded barrel which is what I was looking for. The 1913 rail is also what you would expect from a modern pistol.
The sights are my preferred 3-dot tritium, but they do not clear the suppressor. I don't find this a problem since I am actually more accurate with a suppressor even though it obscures the sights, but something to consider if you expect them to be raised above the suppressor.
Obligatory HK45CT and autosear MP5 host pic: