Quote from: ArtForz on January 23, 2012, 08:54:25 PM

all on the same rig
PhenomII @ 1GHz, PSU is the same SF 80+ gold as used before

5970, linux amd64, cat 11.12, sdk2.5
idle @ 0.95V/157/1000, 182W
idle @ 0.95V/157/300, 152W
idle @ 0.95V/157/150, 149W
cgminer @ 1.05V/820/300, 377W, 761Mh/s
cgminer @ 1.05V/600/150, 308W, 542Mh/s
cgminer @ 1.00V/600/150, 291W, 542Mh/s
cgminer @ 0.95V/600/150, 273W, 542Mh/s

7970, linux amd64, cat 11.12, sdk2.6
idle @ 0.85V/300/150, 115W
idle @ 1.175V/300/150, 132W
idle @ 1.175V/1150/1070, 168W
phoenix @ 1.175V/1150/1070, 363W, 676Mh/s
phoenix @ 1.175V/1150/1375, 370W, 676Mh/s
phoenix @ 0.85V/300/200, 154W, 178Mh/s

7970, windows 7, cat 11.12 7970 edition, sdk 2.6
screen off for a bit,102W
idle @ 0.85V/300/150, 114W
idle @ 1.175V/925/150, 142W
idle @ 1.0V/925/150, 128W
phoenix @ 1.0V/925/150, 235W, 535Mh/s
phoenix @ 0.95V/925/150, 222W, 535Mh/s
phoenix @ 0.92V/925/150, 217W, 535Mh/s
phoenix @ 1.175V/1150/150, 328W, 659Mh/s
phoenix @ 1.175V/1150/300, 339W, 666Mh/s
phoenix @ 1.175V/1150/1070, 368W, 674Mh/s

2MB PCI S3 VGA card, linux
idle 101W

so let's run some numbers, using 0.95V as undervolt for 7970...
whole system:
max OC @ stock V: 5970 2.02Mh/J, 7970 2.01
undervolted: 5970 1.99Mh/J, 7970 2.41

assuming system is 100W (well, more or less...)
max OC @ stock V: 5970 2.75Mh/J, 7970 2.89
undervolted: 5970 3.13Mh/J, 7970 4.39

bullshit calc (aka simple load - idle)
max OC @ stock V: 5970 3.38Mh/J, 7970 3.07
undervolted: 5970 4.37Mh/J, 7970 4.95

Awesome, finally a back-to-back test on the same system... and it looks like the results are pretty close in most of the settings. The "max OC" part is going to vary from card to card, as is the minimum undervolt, so that will def impact the final numbers as well. Did you try going any lower than 950mv on the 5970?