My Phenom 9600 with an 8800gt swaps within 1-2 seconds consistantly. The main window is 1680x1050 and the smaller windows are 560,350 on a 2nd display (same card). This is generally useful in PVE to the fact that my assist macro's still work and I can start casting a spell, hit my PIP Swap and by the time it's done, it's done casting.

For PVP I find this to be unacceptable. If one of the guys goes down, I generally mouse to the window of a live character, hit the new master key for that region and carry on. I don't need details in most cases for pvp, I know the buttons I'm smashing, and I can still see important details on the main characters screen in most cases. I'm very seriously considering 3 more boxes for PVPing @ 70, I figure I'll make that call when I get there.