If you're after the mighty USP, Congrats. You should love it. My first choice, for a guy with normal to biggish hands would be either the .40 or .45 fullsize. These are two different frames, btw, the .40 shares a frame with the 9mm. The .45 is slightly bigger. I have normal sized hands, and I can still control my USP 9mm completely, but I would reccomend that you go handle them b4 purchasing. Neither should be too big, as you describe your hands.
As to caliber choice, you have options. The HK USP is about the ONLY .40 I would buy, for a very good reason. It was DESIGNED as a .40, and was not "Modified 9" as so many other .40's are. So, the .40 is likely to hold up and not go kaboom. They tested the USP with 30,000 rounds of +P ammo, and I believe 6,000 proof loads, and when they got done, they fired it with a bullet wedged in the bore, and it worked fine. Barrel bulged a bit, but it still had tight groups. Check this site for the stats. [url]www.streetpro.com/usp[/url], and click the torture testing link.
So, your .40 should hold up for a very long time, and your wrist will probably give out before the gun does. It's also the only gun where the hipressure of the round doesn't give me reliablity, safety, or longetivity concerns.
The .40 fullsize still has 13 round hi-caps for sale, though they are a bit salty(around $100 bucks apiece). The .45 is limited to 10 rounds, being released after the crime bill. tke your pick. And, yes, the USP is rated for +P+.
Stopping power? 'Bout the same. Whichever works for you. You can pick your loads with these +P+ guns, so .40 or .45, pick a good, respected HP round, like the HydraShok, or Cor Bon, and go with it.
Pick your gun, basically. I would go with a fullsize if it's going to be your primary weapon, but any of the series will serve you well for years to come. My personal pref. is the 9mm fullsize, because of caliber and mag avalibility, 15+1 rounds and the +P+ took care of any wimpy bullet concerns. But, again, pick what suits your likes and needs, you can't go wrong here.
Juggernaut