Number of tables to play?

[winky51]

I am trying to determine the optimal # of tables one can play without impacting their game that much.

1-2 for me is cake for me, its like playing 1.
3-4 is easy since I play only 18% of my hands. I can still watch players and take good notes on all of them. My double monitor allows me to keep all hand histories up to view at an instant.
5-6 I can do but I miss a lot of player info. Takes me a while to get an accurate read on players. I also notice I sometimes mix tables, basically call somewhere I should not. Costs me money.

So what about you people?