6.5 Grendel is an excellent round. I used to have an AR chambered in it. Was a ton of fun out to 600 yards or so, but anything beyond that and the conditions really needed to be ideal for any type of consistency. 6mm BR would very well suited for 1000 yards, as would the 6mm Creedmoor, though like you said, you may run into issues with mag feeding and they will both put you over that 30 grain threshold.

Otherwise, maybe look into a .22-250? Something in the 6mm family would definitely be my preference, though it sounds like you have an idea of what might suit your needs.