Fat 5's are machined polished correct? Meaning they have the fine ridges, like microscopic ruffles, where it was cut...if you don't smooth down those ridges 100% then it won't ever have a mirror like reflection.
High speed is the key too. You can get a polishing kit for a cheap electric drill too, won't work nearly as well as a pneumatic high speed polisher but far more effective than by hand.
http://search.harborfreight.com/cpis...PerPageBottom=
I polished the last 36" of this 3" exhaust by hand with a pneumatic polisher and various compounds, it was bare aluminum before...