Unless I'm way off on velocity(2,200 fps?), I believe an 11.5" 6.5 Grendel shooting 123gr SST doesn't go transonic until 600-650ish. A 16" Grendel would be transonic in the 800-850 range. 22" does only seem to get you another 50 yards before going transonic though. I agree that CM is much better for long distance shooting, but Grendel isn't bad. I think it really boils down to:
Between those two 6.5s, I think Creedmoor by default, Grendel if you want either an SBR or a light weight AR hunting rifle.
Agreed!