I wasn't refferring to perfect play, just making more mistakes than normal and playing overall less well. I guess the same concept of increasing earn can still be applied here.

If I had one table open of 5/10 NL and 7 of 2/4 NL, I might do something stupid and open for $35 for example. These are the kinds of mistakes I was talking about. Plus the play at the different limits varies greatly. It is tough when playing 8+ tables of NL to differentiate from one to the other. I usually look at my hand, glance at my position, and press the fold button if I am going to fold and move on to the next table if I might play and wait for the action to get to me before I decide what to do.

So maybe my point is that the mistakes are a little more costly when mixing stakes than just regular multi-tabling, but that might be made up for with your extra earn from higher stakes.