Edit 3:
Retested with the same Q6600 with 1201 bios in the new motherboard. Passed. Flashed with to 1901 and retested. Passed. So it appears the original P5Q-E is a flaky motherboard. What was odd was some of the symptoms, ie artifacts that sometimes occured just prior to the display not responding, was typical of a failing GPU. Not to mention the HD4830 and 7600GT was like rock on that same motherboard. The 260gtx must stress the system differently than the other 2 cards. All other tests prime, occt, and memtest were solid on that same board.
Glad I had extra HW available as I'm unsure how you could narrow it down otherwise without RMAing multiple parts.