Yep, it's a definite, obvious pattern. I already answered the question myself, just adding this.
A single 7970 won't be enough, and it's anything but quiet unless you keep it stock with fan on minimum. It gets annoyingly loud at around 38-40% fan, and hairdryer at 60, leafblower at 80.
Seeing as you don't have a 7970 in your sig, may i ask where you are getting this hair dryer at 60 and leaf blower at 80 noise numbers from?
mine OC's to 1075/1500 with 20% power tune and no increase in noise.