6 x Gigabyte Radeon R9 270 2GB 256 PCI-E GDDR5 OC.
Asrock H81 PRO BTC s.1150.
Intel Pentium G3220 3,0 GHz 3MB cache s. 1150 Box.
2 x Corsair RM Series RM850 850W - CP-9020056-EU
Corsair Vengeance 4GB, DIMM,1600MHz, DDR3, CL9, XMP,Non-ECC, with Heatsink.
HDD Seagate ST500DM002, 500GB sATA III 16MB
Working under Windows 8.1 64 bit system
Taking 1030 W from the wall and making 2,65 MH/s
After undervolting those cards are making 2,9 MH/s taking 1015 W from the wall.
Undervolting using this method can and probably will void your warranty so you are doing this at your own risk (most cards can be undervolted using tolls such like MSI Afterburner but some are locked and can be modded like this). If you are still reading, this is what you will need to do undervolting:
VBE7 - http://www.techpowerup.com/forums/attachments/vbe7-0-0-7b-exe.52628/
GPU-Z - http://www.techpowerup.com/gpuz/
ATIFlash - http://www.techpowerup.com/downloads/2306/atiflash-4-17/
I don't advise doing this with only one card - in case of trouble it will be hard to recover.
1. Make a backup of your VBIOS - to do this run GPU-Z, pick card and save it to safe place, in case you have few different cards or VBIOS versions, make a backup for each of them
2. Modify VBIOS - run VBE7, open your saved VBIOS, and go to performance tab. Change VDDC #0 to value 1000 (it was good for me you need to find your own). Save changed VBIOS to some directory, other then original ones.
3. If you have more than 3 cards some it became little bit complicated. Shutdown your rig - disconnect PCI-E risers (max 3 can be connected, one of them needs to be your main x16 one) - this step is forced because ATIFlash doesn't support more then 3 cards.
4. Start the rig.
5. Unpack ATIFlash, go to directory you've unpacked it,
6. right click on ATIWinFlash.exe and pick Run as Administrator (probably it will take some time to open it, it is normal)
7. Pick one of the cards, open VBIOS you have modified, then pick Program, after some time you will be prompt that flashing was successful (hopefully).
8. Restart the rig and run your mining software (I'm using sgminer), you need to make sure that it is stable, if every thing is ok, repeat steps 5 to 8 for other 2 cards (you can distinguish the cards that have been modified by the VBIOS version shown in program - current version need to be different then the modified one that you've loaded).
9. Now it is time to shut down the rig and change the plugs disconnect 2 cards - leave main x16 connected) and connect 2 new ones and repeat previous steps.
10. After you finished with all of them you will need to shutdown the rig one again, connect all the cards and power it on.
11. If everything is ok, now you have less heat given and smaller energy consumption
12. You can now experiment with miner settings to get more hashes, for me some settings that previously weren't achievable now work as harm
Tip: From my experiments stability can vary on different coins and pools, be aware of this when you will change the coin or poll for the new one e.g when I've mined LTC on wemineltc it was more stable (could get higher hashes) then on DOGECOIN on dogehouse
13. Most important step: BUY ME A BEER !!!