My reply really doesn't answer your querry, but it's my humble observations...
The last two cards I've run; BFG 8800ultra and a Visontek 4870 I've had were quiet (except at startup where the Visiontek stock heatsink sounded like a jet taking off, but the problem is the stock heatsinks performance in a nutshell......well they both sucked at cooling the card.
I have yet to see a good performing stock heatsink & fan, for ATI or Nvidia. I've got a Visiontek 4870 running now, fairly quiet stock heatsink under normal conditions, but 90*c at load was an utter joke. The solution for the Nvidia 8800Ultra was a Thermalright HR-03 Plus mated with a 18db fan, and the solution to the Visiontek 4870 was this thermalright V2: (Slapped a very quiet Noctua fan on Thermalright V2, end of the noise)
If you ask me, replacing the stock heatsink, for me at least was the best solution, it's now quiet and performance is a LOT better than with the stock heatsinks and fan that could easily fry an egg.
Temps below are with the Thermalright and a dead silent Noctua fan