All three you listed are great with the WSM and 6.5 having more sufficient barrel life. Both have some great bullets. Berger has the 168gr VLD (G1 BC .617 G7 .316) and 180gr VLD (G1 BC .659 G7 .337) The 6.5s are a little lower. Both can be run on a short action (7WSM & .260AI) with minimum recoil and manage near .300 win mag ballistics. But if you want a .300 win mag i understand because i want one too lol. The .30 cal bullet's BC really hits it's stride once you the 190gr and up, my favorite is the 240gr SMK with an acclaimed G1 BC of .771 if you could push them 2950fps, your looking at the bullet staying supersonic till 1500yds

, of course the other's will just about do it too. But sometimes you just need to fill that magnum niche. And while i prefer short action cartridges, there is nothing taking the .300Wby out and watching it kick dust everywhere, while hearing the distinct "shing" of ejecting that magnum casing