A couple of others have already asked what you will be using the rifle for and what game are you going after? That will help narrow it down. Looking at your avatar, I'm assuming you reload. If that is true, I would suggest the 6.5 Sherman Short with a 1:7.5 barrel. That will push the 6.5 heavies over 3000 fps. If you already have dies for the .270 WSM, keep it and throat it for longer bullets. If you don't reload, keep it a .270 WSM or rechamber to a 6.5 PRC.