Roscoroo, the machine is in a full tower case, liberally festooned with fans, so there is lots of air flowing around everything. Plus, the dust filters on the intakes are checked regularly, as are the heatsink/fan units on the components (Zalman copper monster on the CPU, Swiftech copper/aluminum on the chipset). The video card is just a week old, so it hasn't had time to grow dusty.
Skuzzy, I'll email my DxDiag output to you. In the meantime, I'll down-rev the video drivers and let you know what happens.
Thanks!