I run 5 on a 4.3GHz(OC) i7-36something and an NVidia 460GTX. I have to run them all on the low-rez renderer and set the alt windows to limit framerate to 10fps in the background to get any kind of reasonable proximity to 60fps on the main. This is with a stacked-fullscreen-noswap-avoidtaskbar setup with a dxNothing window on my second monitor that shows the alts.