What is your purpose for the power boost from .308 to a 300 Magnum? Are you planning on hunting somethinglarger than an elk at distances beyond 300 yards? If not, you really don't need the extra power (and noise and recoil and increased potential for developing a flinch) of a 300 Mag.

If you want to review ballistics, both Remington and Winchester have ballistics tables for their ammo on their web pages which will give you an idea about the power levels of the various 300 Mags, as well as comparisons to what you've already got.