Which one is more accurate?  Is there any more differences between the two besides the tactical has longer threaded barrel, adjustible sights, better trigger?  Thanks

While I am just guessing on the accuracy, I would imagine there wouldn't be any noticable difference between the 2. I hear the tac trigger is reason enough for the upgrade. The Tac is really made for suppressors, thus the raised sights (to see over the suppressor) and threaded barrel. I would get the tac personally, just because once you shoot with a suppressor, you will want one. I think a .45 Tac is going to be my next purchase

The Tactical also has the match trigger and o-ringed barrel.  While the o-ringed barrel in theory aids in accuracty, IMO the better accuracy you will get (and you will get it) with the Tac has more to do with the match trigger and better target type sights rather than the o-ringed barrel.  I say in theory because while from a bench rest machine the Tac will be more accurate, but in the real world when being shot from human hands the USP is already more accurate than most shooters so the increase in accuracy the o-ring offers is pretty much wasted on mere mortals.