not rereading it all:
is the problem the same on VGA and DVI?
the card draws power through the mb only?
Yup, just uses motherboard power. I haven't tried DVI but because the video output appears perfectly clean most of the time I doubt that's the problem.
Just played the rest of the shareware episode of Quake in GLQuake at 1024x768 without a problem. On the other hand Return to Castle Wolfenstein ran for about 5 seconds at 640x480 before crashing out.