9mm is hard to suppress because of the general supersonic nature. However, if you shoot subsonic ammo, it will be fine, 147 grain JHP for example. Normally, 115 grain is supersonic, but in my experience, winchester white box is almost subsonic, probably coming in around 900+ fps. The reason I say this is because when I ran it through the MP5 with an attached AAC can, it was pretty quiet. If it was true supersonic, it should have been louder.
Now, generally, people suppress the .45 pistol, either the USP Tac or the SOCOM. The Tactical and SOCOM are REVERSE in threads. You will be better off getting a Tactical as you can also get the USPC45 and a threaded barrel and use the suppressor for both.
Suppressors imo do not put that much more wear on the gun, esp. the USP Tactical or SOCOM. The SOCOM is a beast and it can take a beating as can the USP Tactical in .45
All this being said, you can get a threaded 9mm USPC barrel from Jarvis or CCF. Suppressed shooting is alot of fun, especially if you use subsonic ammo.
M