Well you hit the nail on the head, the 45 is probably the best semi-auto sidearm cartridge out there today. It gets the job done effectively and consistently. A Sig Sauer 220 is a very good gun, i wouldnt be second guessing the purchase. If you had the money you could just go out and buy the 10mm also and then you would have both of them. Cooper, the 1911 guy, actually really liked the 10mm, so the 10mm should be a good cartridge, but since you got the 45, you should be set.