That exactly what I saw when my card was overheating, which I suspect its the GPU itself.. wierd gemetry problems... Did you try cleaning it out, especially under the top plate that covers the heatsink? It comes off in 3-4 screws.. That solved my heat realted problems.. Even if you keep a clean case, the dust still collects under the top plate.
Although my card and systems runs normally hotter than those temps u posted, and is still stable.
Best way to check vid card temps while under load is to run rthdribl http://www.daionet.gr.jp/~masa/rthdribl/
Run that in a window, with your temp readings in another window.. You'd be surprised how hot you can get in 30 mins.
EDIT: I'm wondering if that exhaust fan right over your vid card is creating some weird turbulence effect? Maybe not..