F3-12800CL9D-4GBRL and ASUS M4A79XTD EVO no problems

[Joebakb]

That's what I kept thinking, but I've had two separate PSU's and the problem has remained constant, unless there is some problem with the motherboard power-wise.

Antec Earthwatts 500
OCZ modXtream 700w

[Tiribulus]

Yep, that is a zinger. Rereading it I can see why you might suspect a driver issue. Shutting down or rebooting when starting a 3D game that fires up the video card is classic weak 12v rail behavior, but you would think especially the OCZ unit would be fine and having it go away when going to an Nvidia card seems to eliminate power unless both ATI cards were pulling significantly more amperage than the 8600gts.

[Joebakb]

You pretty much hit the nail on the head. I'm going to see if I can snag someone's multimeter before I head back home this weekend to see, but I'm going to wager that everything will turn out just fine.