RE: 7mm Rem vs 300 Win Mag
A good deal of gun writers feel the 7mm is an inherently accurate caliber. A quick look at the BC and SD of the 150 gr 7mm and the 168 gr .308 has them running pretty similar.
So on paper, it would appear as a toss up. I didn't look at the energy at the various ranges so I won't comment on that. But for extreme long range shooting I would probably opt for the 30 cal.