As long as I can tweak it I would use a TT-33 Tokarev in 7.62x25. The round has an effect range out to 100 meters with a pretty flat trajectory all the way out according to everything that I've read.
Everyone that I talk with concerning the gun/round states that the recoil isn't much, somewhere along the lines between a 9mm and 40 S&W as long as you're not using submachinegun ammo.
The mag carries 8rds but most competitions that I've ever been in require a reload after 6 to be fair to the revolver guys. So a high capacity to my way of thinking isn't a issue.
The gun has been proven on countless battlefields as rugged, simplistic, dependable, effected and has the same basic ergonomics as the 1911.
The tweaks that I would make if possible would be of course a action job, refitting of the barrel (after adding a screw on compensator) to the slide as well as refit of the slide to frame. I would flare the mag well as well as flaring and lowering of the ejection port. Add to that stippling of the front/back straps as well as the rear of slide, plus the addition of XS 24/7 express sights (small dot) and I would be good to go.
Except for IDPA (I don't believe they still allow compensators, thus a need for a backup barrel and bushing) or those who feel that they need to put limits on calibers
fire
I would find it hard to beat!