I am running 5.5 here in 93 octane sea lvl Maryland,
feels great, definitely noticible difference from 3.5, 4.0, 4.5 and 5.0.
I tried each of them for a couple runs on highway, 5.5 felt the best, and I am planning on leaving it this way for good.
No I am not running race gas or octane booster.