I have an APC 1500 something or other, with both my boxes on it. So it is running a dual core with a 5870 in it and an I7 with 2 275GTXs. If I plug in the monitor also it starts beeping at me so I'm right on the edge. I just turned the beeping off and leave the monitor plugged in. It will only keep them all running for 3 or 4 minutes if the power goes out, but it does keep me from losing a day of crunching every time the power blinks off for 3 seconds.