I shoot a USP45f in L10, and usually do okay (don't talk to me about stage 4 today). The USP is also my duty gun, and I quite like it - accurate, NEVER jams, fairly fast, and it's fun to beat people with a weird (for IPSC) gun. I know I'll get an STI/custom eventually, though.
I've made B class, just barely, but I can tell you what works for me with a USP.
First - reload for power factor and recoil impulse. 165-170 pf is much easier to control than 180-190, and different powders/bullet weights feel different and work differently.
The stock sights are okay, but I've found that thinning the front and opening the rear up help a ton with speed of aquisition and a bit with accuracy. I have long arms, which exacerbates. My front sight is at .120", which is as thin as one can go with my duty Trijicons. My rear is opened to .160". Start by thinning the front, then open the rear if you feel it's necessary. Stock are about .130 front, .150 rear.
Skate or stair tape helped me quite a bit. I put 3M stair tape on the frontstrap, under the trigger guard, and on the sides of the grip. I put skate tape on the backstrap, as the stair tape was too grippy to adjust my grip quickly if my draw wasn't right.
You have to shoot high thumbs, just like a 1911/2011 platform. I've installed the safety/no decock plate ($10 and two minutes) to avoid inadvertant decocking. My long monkey thumbs required trimming back the slide stop, as I occasionally bumped it, and while it never caused a problem I didn't like it (another $20).
The Match trigger group (about $100, and easy to install yourself) is WONDERFUL, worth every penny.
Enjoy the games and your new gun!