Long story short, for 2nl after rakeback at Full Tilt you're paying about twice the rake as at PokerStars, pretending you don't even earn FPPs. Full Tilt before RB is abot $0.0038/hand of rake and about $0.0028/hand after rakeback, while PokerStars is about $0.0014/hand in rake.
If people would like to post 5nl and 10nl samples (list 6m or fr, # of hands, MGR over that sample) that would be cool.