Just an update. Turning on 1.4v to the core made me experience that "freeze, but mouse moves" problem that many other people are reporting. What is funny is, the card will recover gracefully after about 20 seconds or so, run for about a minute, then repeat the cycle. Makes me wonder if the people who experience this problem, can fix it by lowering the core volts on their cards..?
In the end, I put my card back to 1.2v, 375MHz/900MHz and it has run a 3DMark loop for about 8 hours straight. Also got some Quake 4 time in, and ended the last 3 complete levels (and the game!) with no visual or framerate problems.
I have a kid looking at that mem voltmod pic, and maybe over the weekend I can convince him to do the soldering for me.
Thanks for reading.