I have done some long range prairie dog shooting, out to 900 yrds plus. I think any of the calibers you mentioned would work fine with the best high bc bullets you can find for that caliber, Hornady A-max, Berger, or Sierra Match King and the like. The problem is more in the optics and your ability to estimate range. The optical quality of a scope and magnification become critical at 1000 yrds. A really good range finder is an absolute must with a tri-pod mount, at that range you cannot hold a range finder steady enough on a pd mound to get a good range estimation. A missed range estimation of just 25 yards at that range is a complete miss by several inches at 1000 yrds. A good muzzle brake and a very heavy rifle will help lessen recoil so you can see your bullet strikes. I have used a 6mm Remington with 105 grn A-max's, but I am thinking that a 22-250 AI with a 1 in 7 twist will be my next long range build. By the way you should try a 204 Ruger as your main caliber, its flatter shooting than the 22-250, better in the wind, less recoil, less powder, which means longer strings of fire before the barrel gets too hot to shoot.