Hmm...very strange. If it were multiple PCs, I'd have some other things to check. With all of 'em on 1 PC, it negates a lot of the connectivity/networking aspects. What sort of broadband connection are you on?

Also, have you tried clicking one window and then another one to see if it fixes the FPS issues?

Regarding the 1 account going nuts with latency, what happens if you run just 4 accounts?