Don't bother with a large frame AR, and get a 6.5 Grendel. I've been using a steady diet of 123gr A-MAX on top of 31.2gr of CFE223 from my 16" Grendel, and I get 2500fps with it and that load. The gun is very lightweight, well-balanced, and favors portability, while having a lot of practical accuracy.
I also have a .260 Remington AR with a 22" barrel. The complete upper receiver of the .260 Rem is heavier than the entire 6.5 Grendel with scope, mount, and a mag (8.6lbs with 2.5-10x44 Viper PST). I love them both for different things, and use them both.
The real main benefit is that I can shoot high quality, factory ammunition specifically designed to work in an AR15 at much lower pressures with the correct burn curve in the Grendel, compared to FGMM, Black Hills, Corbon, Nosler, etc. for the .260 Rem, which I won't even let near my .260 Rem gasser, making it a reloader's rifle only for me.
There are only a few factory loads that do well for target work that are specifically meant to work in the AR15 in common calibers from major manufacturers:
* Mk.262 77gr SMK stuff for the .223/5.56
* Maybe some other .223 Rem match loads, but many are meant for bolt guns
* Everything 6.5 Grendel that's a target load
Name me one factory load that is specifically meant to run in a .260 Rem AR10 with the RLGS and 20-24" barrels? Now if you're talking about a 16" barrel, what gas system length are you considering? You basically will need to seriously constrain the gun to shoot either lightweight pills with a fast-burning powder, or really dial down the charge weights with fast burning powder and longer pills. It's basically a dead end from a practical perspective in my opinion, and my statement comes from years and years owning AR10's in .260 Rem, as well as 5 years of working with the Grendel.
I basically have a load that tracks like a 175gr SMK from the .308, with ~half the recoil, and a much lighter, shorter gun, that has more affordable match ammo for it, is more affordable to load for, and doesn't require any crazy large frame parts, just standard AR15 receivers and bolt carrier, with a Grendel bolt, mags, and barrel. This is why it killed .308 for me personally, and I still have 85% of the energy on target of a .308, even with the higher BC pills from longer barrels in the .308. These are real results that I have been able to witness first-hand.