The Creed will out perform the Grendel and you won't need a 28-30" barrel to do it. Bullets are a wash, both shoot high in the BC arena. A 22-24" AR10 in a 6.5 Creed will manage 2,700-2,850fps shooting 140gr hybrids. Run the ballistics, you're supersonic beyond 1,400yds.
Ok, I'm just throwing this out there for discussion.
If the 6.5 Creed will only run 2850 with a 140 grain, why not stick with the 30-06 shooting the same bullet at over 3000? Bolt gun, yes.