6.5 Grendel has got good legs out past 400 yards and excellent bullet weight options for varmints to mid-sized game.
Question: Will it have enough knockdown to take antelope / whitetail deer out to 400 - 600?
Short answer is yes!
More detailed answers can be got by reading the Grendelmania
series and by getting the grendel-dedicated reloading handbook. There is an overview at 6.5 Grendel Reloading Handbook, Volume 1