If you want a silent GPU you have 4 options:
1) put your pc in an closed cabinet under your desk -> i am dead serious, there are several desk models that can do this (IKEA) an will solve all your problems (beware of heat though)
2) go liquid, Powercolour has an LCS version of the 7970, that makes it the quietest + fastest GPU around
3) get a decent aftermarket solution (MSI twin frozr etc), remove the fans, strap on 2x 120mm fans (like Nexus) and set them at 7V
4) buy a decent aftermarket solution and flash the bios to a minimum fanspeed of 10%
Personaly I am very happy with nr 3: I have a deadsilent 580GTX.
Remember that the latest stock AMD/ATI 7xxx series are "reasonably" quiet as-is.
I have the HD6950 with Accelero S1 and 1x120 Scythe GT strapped on. Unfortunately the S1 heatsink is a little weak and i have some BSOD issues that i believe are caused by the GPU. I am thinking of your solution #3 for my next GPU. Would 2 scythe GT 800rpm be equivalent to Nexus? The scythes actually run about 900rpm@12v but i need the fans to be able to handle cooling down a card from a critical temp if need be.
I am hoping that for the next gen AMD will have even cooler 8800 series card. That way i might not even have to change the fans rather i can just settle for aftermarket solution and hopefully the aftermarket solutions have gone up from 92mm fans to 120mm fans.