I can't imagine that switching backwards and forwards between limits is helping your game. Not only can you not get a consistent feel for each limit (close in quality thought they may well be), but it also implies that there is some psychological factor behind which BB you choose. Stick with one (the lower one in all probability) and move up a level when you can afford to (i.e., by implication, when you've become a consistent winner at the lower level).

Secondly, it sounds like you're playing way outside your bankroll. Even if you minimise variance by avoiding high-risk/tight margin plays, variance WILL still bite you on the arse. What happend when this $100/$300/$400 is gone? Will you just reload as if nothing happened? Or will you be banned from the tables forever?