Tiny PE -> MBA -> BB FSG Associate -> Large PE?

I'm still in banking but i'd imagine your better off just trying to lateral to another PE firm then doing banking.

Chances aren't good. People don't generally move up within PE in terms of fund size. It's generally much easier to start at megafunds or large MM funds and then lateral and get more senior positions (i.e. senior associates / VP) at smaller firms.

Of course, it isn't impossible. I know people that have gone from MM shops and moved up. As for you, the move would be extremely since you're going back to IB (why are you doing that, btw?). Why would a megafund or large MM PE fund hire someone that's been doing IB when they can hire someone that's been doing PE?