When you say "at the wall" you mean using an external watt meter?
Here's a pic:
Here's an update, I upgraded to latest firmware 2.5.57 and tried some more undervolting. At 0.59, some chips refused to start working, or would turn off after half an hour. So I just used 0.6, bumped up the fans to 100% and let it run for a few hours, then took pictures of the watt meter.
Temp Front / Back T,B 28 °C / 40,39 °C
Fan Speed 100
Start Voltage 0.6 / 0.6 / 0.6 / 0.6
Max Voltage 0.6
Max Watts 120 / 120 / 120 / 120
Hardware Version SP20E Jackson
FW Version 2.5.57
CGMiner Version cgminer4.7.0
754.63 GH/s
5 min GH/s 869.91386
That's 321.7 watts, at the meter.
Using the first GH/s number I get 0.4263016312630031 watts / ghs.
Using the 5 min number (which changes often) I get 0.3698067300594567 watts / ghs
The asic page reports the following:
LOOP[0] ON TO:0 (w:403)
0: DC2DC/1/:[vlt1:593 vlt2:597(DCl:794 Tl:794 Ul:597) 29W 48A 35c] ASIC:[ 85c (125c) 440hz(BL: 440) 180 (E:193) F:0 L:0]
1: DC2DC/1/:[vlt1:591 vlt2:597(DCl:794 Tl:794 Ul:597) 34W 57A 41c] ASIC:[ 85c (125c) 510hz(BL: 510) 223 (E:193) F:0 L:0]
LOOP[1] ON TO:0 (w:432)
2: DC2DC/1/:[vlt1:593 vlt2:597(DCl:794 Tl:794 Ul:597) 33W 55A 44c] ASIC:[ 85c (125c) 500hz(BL: 500) 207 (E:193) F:0 L:0]
3: DC2DC/1/:[vlt1:595 vlt2:597(DCl:794 Tl:794 Ul:597) 34W 58A 45c] ASIC:[ 85c (125c) 510hz(BL: 510) 225 (E:193) F:0 L:0]
LOOP[2] ON TO:0 (w:343)
4: DC2DC/1/:[vlt1:593 vlt2:597(DCl:794 Tl:794 Ul:597) 32W 54A 36c] ASIC:[ 85c (125c) 480hz(BL: 480) 167 (E:193) F:0 L:0]
5: DC2DC/1/:[vlt1:593 vlt2:597(DCl:794 Tl:794 Ul:597) 30W 50A 38c] ASIC:[ 85c (125c) 450hz(BL: 450) 176 (E:193) F:0 L:0]
LOOP[3] ON TO:0 (w:427)
6: DC2DC/1/:[vlt1:595 vlt2:597(DCl:794 Tl:794 Ul:597) 34W 58A 42c] ASIC:[ 85c (125c) 500hz(BL: 500) 218 (E:193) F:0 L:0]
7: DC2DC/1/:[vlt1:593 vlt2:597(DCl:794 Tl:794 Ul:597) 35W 59A 44c] ASIC:[ 85c (125c) 520hz(BL: 520) 209 (E:193) F:0 L:0]
[H:HW:754Gh (500),W:264,L:0,A:8,MMtmp:0 TMP:(28)=>=>=>(40,39)]
Considering that it is placed in a backroom and I live in a tropical country, I think I have achieved some pretty impressive numbers. All I need now is for Santa to take me to the North Pole and we'll see how much this thing can crank out.
My second 1000 watt PSU is on stand by, I may do an overclock (turbo) test later and see how high I can get this time.