I know your just asking about cash games, but considering you haven't received any response to you question, I'll through in my personal opinion which could help.
I'm not a fan of more then 2 games at once. Occasionally, in the beginning of a mt tournament, when I'm real tight killing the first hour or so, playing only strong hands and recognizing where the bad players are sitting; I'll jump on a full table sng. If I'm just playing sng's, I'll start one, and if I'm still there when half the players are gone, I'll start a second one. While the short table is picking up momentum, the full table is at its slowest. If I'm into a 4 or 5 hour session, I'll keep starting a second one after one finishes of course with the same gap. If you hit the board a couple times in a row, the timing to start second game seems to be right on target. In a 5 hour session usually end up with 9 to 11 sngs. When its time to start a second game, I'll jump into any table that's filling up quickly with between $30.00 and $100.00 buy-in. If your finishing more then 11 games in a 5 hour session you're probably not having a good day. Even if I was planning on a 5 hour session, I've been known to pull the plug in less then 3 hours. Many days won't be good ones. If on a good run, will occasionally jump into a bigger game.
This is the only way I find myself playing my best game and being a contender. I've tried 3 and 4 games several times in the past, and always made mistakes, or found myself just playing the cards dealt to me. I believe while playing online it's critical to locate the bad players, along with betting patterns opponents occasionally give away. These rare tells
online take time and attention to recognize, and hope that your right when you try to use them. Playing 4 or more games your obviously playing more of a percentage game based on your pocket cards.
I know there's plenty of different software support programs we use, that track our play and our opponents making online some what easier with so many different players we face. Although this information is helpful, I like judging my opponents play based on how their playing today, right now at my table. Players games can improve quickly online, and my software may not recognize it quick enough. I may have played someone 30 times in the past, but haven't seen him in months.
I know of two guys that play multi games as a team side by side with a few computers. One plays the games, while one feeds all the known information into a program, which I'm going to assume is an illegal bot. They play either the percentages or the bots recommendations. When I see one of them, I always ask how their doing, and never seem to get a straight answer, or ever found out what the program was they were using.
I've read of people playing 6, 8, and 10 games at once. I would suspect some super programming going on there. It has to be percentage play. Don't know if that strategy works. But I know I wouldn't even consider it.
As you could see I'm also not a fan of cash games online. Although I dabble in them when bankroll looking good, never seem to do well with it except for the occasional strike. Yet, love them live. To many different things going on with cash games online. Thats another topic in itself.
Anyhow, good luck with what ever you do and keep us posted.