If you really want to compare apples to apples we'll keep things as close as possible. I'm concerned with Ballistic Coefficient more than anything. The higher the BC the better the downrange energy and less wind drift. I believe that’s what we’re all concerned with. A Sierra Game King bullet in a .308 200 grains has a BC of .560 and a .338 215 grain has a BC of .565. Big deal, virtually no difference.
Now let’s take a Sierra Match King. .308 240 grain Bullet has a .711 BC and a .338 250 grain bullet has a BC of .585. Now that is a big difference and the .308 comes out on top. One could argue a .338 has a 300 grain bullet, this takes equality out of the equation. Might as well throw a 50 cal in at that point.
Like I said a 30 caliber is hard to beat.