I know it's not really fair to blame all video card problems on chipset manufactures, but I have had far more trouble with ATI video cards than Nvidia.
i think that's been discussed in here somewhere, but i'm not going to search for it! i've never had any trouble with either amd/ati or nvidia, except my nvidia frying itself in the laptop (but that was common with the 8600M series).
tough break jake, any idea what changed recently? you did have those two 6970s playing nice with each other for a rather long time, so them not getting along now is a bit weird :S