Breaking pairs up a bit more:
-calling 3b - pairs 66 and down, -0.66 bb per hand (255) - profitable
-calling 3b - pairs 77-99, -3.52 bb per hand (243) - not profitable
Clearly I'm peeling the higher mid pairs preflop and then not finding the fold button early enough post-flop, whereas I'm easily playing set or forget with 22-66.