I'll take the 570 over the 6970...
570 very quiet card compared to the 6970 both very good cards, because the 570 was cheaper i gone with it to replace my dead 4870x2.
The 5xx cards very quiet over the 6xxx line from what i used so far.
Not quiet by much:
Still a GTX 570 in the lower $300 range is a great buy and offers just as much performance as a HD 6970 in the higher $300 range.