Go 1/9" in the 6x6.8 barrel.
I built a 6x6.8, 22" heavy sporter 1/9" tw bbl on a Savage action.
The ar15 I built 1st was 22", 1/10" tw, the 1/9" seems a bit more accurate with the same loads.
22" lenghts will spit a 55-65g at 3400-3500+ fps,70g at 3000 fps, 80g to 87g at 3000, 90-95g at 2700-3000,
My pal ordered a 243 & 7-08 bbl for his Ar10 builds, 22" & threaded.
Im debating 2 more savage barrel myself.