I haven't actually experienced it in the last week or so but while browsing (nothing heavy, even on facebook) screen would just go black and then into stand-by as if it were not getting a signal. I was getting some artefact also using revit. I've ran furmark for 10-15mins and temps stayed under 100 as the fan ramped up, not weird artefact either.
Sometimes artefacts show up in games when Furmark shows no problem. You say under 100C but how far under? Keeping things under 80C is better and I have seen artefacts as low as 85C. It'sd probably not a card worth spending money on now as aftermarket cooling solutions most likely won't fit and it's TDP is pretty massive.
Mines the 320mb model as far as I'm aware.
In that case it's one of the earlier ones which is more or less the same performance wise as the 8800GT.