If it's just poker then I can play between 9 and 12, If I'm drawing something or got some other things to do then it's just 6 tables - on the secondary monitor. Used to play up to 16 tables, had APM tester installed (Actions Per Minute) and was able to keep around 130 APM during first 4 hours, then APM starts to fall down... fingers getting tired. More than 16 tables is hard to play, I guess larger screens and better setup are needed.