Didn't know they made them in 6.5 Grendel. Creedmoor yes, but not Grendel. Had to look it up but sure enough, they do.

Given the choice between the two cartridges, I'd probably pick the 6.5 Grendel. With bottleneck cartridges, I'm partial to a hair more bullet mass than the .243" caliber provides. I had a 243 Encore pistol years ago, but I could never get it to shoot that accurately with the 95 and 100 grain bullets I tried through it. The 85 grain Interbond did well, though. I think the 1-10" twist coupled with the lower velocity created by the shorter barrel meant the heavier bullets didn't stabilize well.