If you're going to get into USPSA decide how far you're planning to go with this. If you want the good scoring, and to go far, you'll want something that meets major power factor. That rules out 9mm for either the open or limited class pistols. Meeting major power factor DOES have advantages over just meeting minor power factor. I easily got to major with my 1911 wide-body in .45 ACP with 255 grain projectiles moving at about 700-725fps. Soft, and little, recoil gave me fast follow-up shots on double tap targets. It also got me onto the next target quickly, and smoothly.
If you want to learn more about either USPSA or IDPA come up to PF&G this Sunday. At the raffle drawing there will also be people on hand to answer questions about both competition types.
BTW, when I was shooting IPSC there were at least one course per competition/day that required reloads after 7 or 8 shots. Which negated any benefits from having higher capacity pistols. I knew plenty of people with single stack 1911's that would smoke people using double stack pistols (grocks)...