Thanks btcnut, this is what I was looking for. I have 3 7970's just cranking right now and stability is more important to me than purely maxing out the motherboard.
Sounds like 4 x 7970 might be the trick.
What power usage are you getting out of a 4x7970 set-up ?
I can get as low as 605w @ 925mhz if I downclock and undervolt
I run at about 650w with slight overclocking (while undervolting a little less) on the good cards to get about 580mhash/sec @ 162.5/w/card on average
I have 6 rigs with 5 cards each. I run them at 930/680/0.937v they pull about 850watts at the wall (~2750Mh)
before i started downvolting with msi afterburner during the winter. the same rig pull 1400watts at 3300Mh
I tried to get 6 to work.. I could NOT. windows would load the device, but not the drivers. that being said, someone i know DID get 6 to load.
edit: cgminer does not report the proper voltage.
cgminer version 2.3.6 - Started: [September 16, 2012, 5:13 pm] Rig:miner17
miner17
(5s):2753.89 (avg): 2752.06 Mh/s | H: 114.4 Q:190937 A:291407 R:2095 HW:368 E:?% U:34.57/m
TQ:? ST:410 SS:? DW:21871 NB:1886 LW:666670 GF:217 RF:1652
Connected to http://gpumax.com:8332 with LP as user ?
Value:
GPU 0: 74.0C 3254RPM 50% 124 | 550.6/550.5Mh/s | 97% | 930Mhz 800Mhz 1.17V A:58514 R:306 HW:0 U:6.94/m I: 9
GPU 1: 73.0C 2166RPM 36% 109 | 551.0/550.5Mh/s | 97% | 930Mhz 800Mhz 1.17V A:56124 R:927 HW:368 U:6.66/m I: 9
GPU 2: 73.0C 2388RPM 40% 113 | 550.9/550.5Mh/s | 97% | 930Mhz 800Mhz 1.17V A:58462 R:296 HW:0 U:6.94/m I: 9
GPU 3: 74.0C 2560RPM 41% 115 | 550.4/549.9Mh/s | 97% | 930Mhz 800Mhz 1.17V A:58980 R:291 HW:0 U:7.00/m I: 9
GPU 4: 73.0C 2113RPM 38% 111 | 551.1/550.5Mh/s | 97% | 930Mhz 800Mhz 1.17V A:59327 R:275 HW:0 U:7.04/m I: 9
edit2:
I run one of my rigs at 950, i dont know the exact watts
clock: 950/800/0.949v
cgminer version 2.3.6 - Started: [September 17, 2012, 9:05 pm] Rig:minerwb
minerwb
(5s):2806.69 (avg): 2797.62 Mh/s | H: 126.4 Q:162541 A:235231 R:1222 HW:0 E:?% U:34.6/m
TQ:? ST:414 SS:? DW:18328 NB:1502 LW:503642 GF:224 RF:1635
Connected to http://gpumax.com:8332 with LP as user ?
Value:
GPU 0: 73.0C 2389RPM 40% 113 | 561.1/559.5Mh/s | 99% | 950Mhz 800Mhz 1.17V A:46758 R:229 HW:0 U:6.88/m I: 9
GPU 1: 74.0C 2882RPM 50% 124 | 560.9/559.4Mh/s | 99% | 950Mhz 800Mhz 1.17V A:46820 R:266 HW:0 U:6.89/m I: 9
GPU 2: 73.0C 3573RPM 56% 129 | 561.4/559.6Mh/s | 99% | 950Mhz 800Mhz 1.17V A:47345 R:228 HW:0 U:6.96/m I: 9
GPU 3: 74.0C 2468RPM 44% 118 | 561.6/559.5Mh/s | 99% | 950Mhz 800Mhz 1.17V A:47274 R:269 HW:0 U:6.95/m I: 9
GPU 4: 73.0C 4631RPM 75% 148 | 561.6/559.6Mh/s | 99% | 950Mhz 800Mhz 1.17V A:47034 R:230 HW:0 U:6.92/m I: 9