6.8 sub loads new AR build

[Bigshooter]

I'm thinking about a dedicated AR upper strictly for sub loads. I originally had my sights set on a 300/221 but I started thinking about using the 6.8 instead, mainly due to the fact that the cases are easy to find and I already the dies and such for it.
Was thinking a 1:8 twist-10" barrel with, 150-160 gr. bullets.

Has anyone tried this?
Pros-cons?

Thanks in advance