For short range I would rather have a Grendel loaded with 90gr flat-based bullets running around 3000fps, better terminal performance than boat-tails and more secondary effects from the higher velocity, plus I can always switch mags and run heavier rounds for longer range and/or better penetration.
Too many of these "Which round is better" debates are based on a myopic view of what we need, what we need is what is going to win the fight. Yes you might almost never need anything bigger than a 5.56, until you do. I have humped a 7.62NATO MBR rather than risk not having enough gun when I need it, I think the Grendel would be an adequate replacement for that, the 5.56, .300 Whisper, 7.62x39, etc. are not IM (not so) HO.
I want, not just long range, but penetration and the ability to kill targets behind cover, I also want to be able to kill medium to large game and do it out to 600 yards or a bit more, the 7.62NATO does this, I think the 6.5 Grendel will probably do this (and yes I plan to test it well before I switch), the mousegun calibers might do it if Tinkerbell wiggles her ass right, but I don't plan to depend on that fickle little tart.