Great thread, should be a sticky! :P
With regards to the size of the USP being detrimental to EDC conceal carry: yes, there is merit in the argument, but not that much. I am 1.71m (5'7") tall and weigh about 65kg (143lbs?), so I am not a big guy. I EDC a USP9 full size in a CompTac Minotaur IWB, and my lifestyle does not always allow for casual clothing. Mostly I dress relatively smart. I have been concealing successfully in public for just under 2 years now and haven't been made out once.
Is it comfortable? No, but you get used to it. Is it easy to conceal? Not at first, but you'll find a system of carry that works for you.
If you are a prospective USP buyer do not let the size of the pistol put you off it.