Heya Jim,
Sorry, missed the 40% on the first page...been a looong day

I've only seen this issue on a squadmate's ATI 1900 card. Like tamper, I suspected heat at first, but your CPUID shows nominal temps at 74C...(try checking CPUID by alt-tabbing out
while playing and not just after a game. There will be a significant difference I think.)
...unfortunatly...that leads me to suspect bad v-memory.
But before I am convinced of that, A few things I would do if it were me:
...I'd turn everything down to its lowest settings and get the lowest memory usage number I could,(why I asked about it in the first place) and fly a take-off mission and try and keep the load light as I could...and note any difference.
ROF taxes the video pretty hard...
...a complete shot in the dark, but something that helped my own GFX 285 OCX card, was I went into nvidia's control manager and disabled PhysX, since ROF doesn't use it. My card runs alot cooler, although Ming says it didn't make much difference on his. But like a said, a shot in the dark.
Hope this helps,