I had a look at the settings on my 670. When it boosts to 1280MHz the voltage goes to 1.175v. Temps stay around 70c though the fan is low (50%).
I've got a Direct CUII and i'm very impressed with the noise to heat ratio. I gave it a run on Unigine Heaven ( I don't do ridiculous benchies like furmark, i'm never realistically going to use it like that), and i found it stayed around 70C, and the fan was still inaudible to me. I even took deders advice and cranked up the memory to nearly 7Ghz and the temps didn't change much.
I think that's about right for most 670's. Mine wasn't anywhere near as overclockable without a bit of a voltage nudge The cooler is great, it blows down onto the memory chips too.
I could put the voltage up another 50mV but it seems to cause it to hit the power draw max, despite the card being cool. I'd only need a tiny bit more to get over 1300MHz
