I currently have a C2Q / 8800GTS system. I don't really play any intense pc games anymore, so I am in the market for a power-efficient yet modestly powered graphics card. I have no preference as to whether Nvidia or ATI makes it. I think I would prefer something fanless but I am willing to have one with a fan.
I don't like fanless gpus, they can get pretty hot if they don't have a large enough cooler or you dont' have a breeze in your case. The 4670 is a nice card that will even allow you to play some games.
Why not just keep your 8800GTS? you want to spend money on a more efficient card that might save you a couple bucks in power over a year? That's kinda silly. No offense.
He is looking for less power consumption, the 8800 gts 320 uses a lot of juice. Over a few years the savings can add up. Plus, he can turn around and sell the 8800 gts for something, especially to someone who might want to SLI there current 8800GTS.
The idle characteristics of the 5xxx series are nothing short of amazing in terms of power consumption. Obviously when gaming the situation changes and it behaves more as a normal card... but who games 24/7? If this is a PC that is going to be left on 24/7 a new video card MIGHT not be a horrible investment. Most people go after the low powered cards for heat/noise reasons... but hey, to each his own!