I've had a 22-250 with a 1:12 twist and it shot the 50 grain Vmax really well out to 450 yards or so... I would actually say that for shooting 600-700 reliably and consistently, I'd go with the 6.5 Creed. I just built a 260 rem for long range varminting and steel plinking...

I wanted something to buck the wind a bit better than the 22-250 (50 grain pill in 20 mph winds sucks) the 6.5 will do that a lot better.

Just my 2 cents,