I'd say it just depends how fast you want to go. The 215 will bring out the best in all of them
With a 26" barrel you are looking at about:
30-06 - 2750 fps
300 WSM - 2850-2900 fps? (a guess)
300 WinMag - 3000 fps (Broz shoots this combo a lot, with H1000 powder).