Multi-tabling question, how many are enough?

[Smoothcall]

If you are getting rakeback from a site how important is it to play as many games as possible? I have multi-tabled 4 easily. But since i'm getting the rakeback i'm trying loading up on 6 or 7. Do i stand to make more in the long run playing more games? Especially with the extra rakeback for 2 or 3 more games beside the hourly for each game. Or is it conceiveable i could make less money playing too many games by making mistakes such as getting timed out with a winning hand. Or acting impulsively and making a bad play do to being more rushed.

What do you guys think?