I shoot 208s all the time in a 1/12 308Win, and have had good sub-moa accuracy with the Hornady 225gr BTHP at 1/12, 2500 fps as well.

In my 1/10 30-06 I've gone up to the 240gr SMK with excellent accuracy past 1000 yards.

The only place I can see where 1/9 might benefit is if you should ever wish to load heavies at subsonic velocities.