sorry.....

both rigs:
core clock-1090
memory clock-1500
auto fan
no under voltage
and I don't use cgwatcher,so I can't help you with that.......
7970s are running @ 1090 core 1500 mem and you get 770KH/s? :-S
I am running a stock 7970 @ 1065 core 1800 mem and get 740KH/s and an Asus 7970 Direct CU II @ 1040 (higher clocks drop hash rate) and 1725 mem and get 714 KH/s :-S
You use the usual settings? -g 2, 8192, w 256, etc?