Re: 260 rem or 308 win for new build
I have a .308 and a 6.5x55 (pretty much the same ballistics as the .260) and have shot them side by side out to 600 yards. Even at 600, the 6.5x55 is noticeably superior to the .308 in terms of trajectory, wind drift, recoil, and general shootability.
However, I have been shooting my .308 more because I have a ton of reloading components for it and because I am trying to work on my wind/mirage reading and doping skills. The .308 is less forgiving of a bad wind call, which makes it a better teacher IMO. Once I have mastered my .308, I will be that much better with my more capable rifles.