Finally got round to this tonight! had a bottle of wine to steady the nerves for a BIOS update of over 1k GBP worth of GPU's and I must say,

OH MY GOD!!!!!

I have been chasing 750Kh/s for a little while for no other reason than when the 4th goes in I want 3Mh/s out of it :) so I'm mucking around and reading this and that, (I'll drop all the links in the bottom of this post) and finally manage to get it .75Mh/s per card 8) I'm only running 3 at the moment waiting for a longer riser to turn up. But yep all 3 are running .75 and I'm a happy little boy, its cost me 20W at the wall but who cares?

Then the wine kicks in and I decided that tonight is the night I'm going to flash my BIOS and under volt these things! Needless to say from my general tone I've not been left with a pile of scrap GPU's :)

Heres a little table for you, please read the numbers carefully as they don't always follow due to not trying every conceivable combination of the kit I have here.

[table]
[tr][td] No Cards [/td][td] Kh Rate / Card [/td][td] Engine Speed [/td][td] Mem Speed [/td][td] Voltage [/td][td] Watts [/td][td] Kh/Watt [/td][/tr]
[tr][td] 1 [/td][td] 750 [/td][td] 1090 [/td][td] 1500 [/td][td] 1.2 [/td][td] 340 [/td][td] 2.206 [/td][/tr]
[tr][td] 1 [/td][td] 750 [/td][td] 1090 [/td][td] 1500 [/td][td] 1.081 [/td][td] 304 [/td][td] 2.467 [/td][/tr]
[tr][td] 1 [/td][td] 750 [/td][td] 1090 [/td][td] 1500 [/td][td] 1.075 [/td][td] 302 [/td][td] 2.483 [/td][/tr]
[tr][td] 2 [/td][td] 740 [/td][td] 1070 [/td][td] 1500 [/td][td] 1.2 [/td][td] 651 [/td][td] 2.273 [/td][/tr]
[tr][td] 2 [/td][td] 750 [/td][td] 1090 [/td][td] 1500 [/td][td] 1.081 [/td][td] 574 [/td][td] 2.613 [/td][/tr]
[tr][td] 2 [/td][td] 750 [/td][td] 1090 [/td][td] 1500 [/td][td] 1.075 [/td][td] 564 [/td][td] 2.660 [/td][/tr]
[tr][td] 3 [/td][td] 740 [/td][td] 1070 [/td][td] 1500 [/td][td] 1.2 [/td][td] 960 [/td][td] 2.313 [/td][/tr]
[tr][td] 3 [/td][td] 750 [/td][td] 1090 [/td][td] 1500 [/td][td] 1.2 [/td][td] 980 [/td][td] 2.296 [/td][/tr]
[tr][td] 3 [/td][td] 750 [/td][td] 1090 [/td][td] 1500 [/td][td] 1.081 [/td][td] 843 [/td][td] 2.669 [/td][/tr]
[tr][td] 3 [/td][td] 750 [/td][td] 1090 [/td][td] 1500 [/td][td] 1.075 [/td][td] 830 [/td][td] 2.711 <---- Very unstable![/td][/tr]
[/table]

I can't make a more than educated guess on temps and fan speeds as I didn't record them, as it's a little unfair with a lot of environmental variables coming into play, rig shutting down cards cooling, only x cards running instead of y cards ruining, me in the room, heating cutting out, door open, more wine, etc. But the educated guess says everything is running cooler and the fans aren't working any where near as hard as they used too.

I will buy a raffle ticket for the February draw for the 1st person to guess which config I'm running 8)

I will update when the 4th goes in mid week, well at least to show it's output running undervolted, as I'm not going to flash everything back just for testing.

I might push this a little further and see how low I can go and stay stable at a later date, and will also try a BIOS from The Stilt when I get a little more time. But for now I'm a happy little miner :)

UM

LINKS

http://www.cryptobadger.com/2013/10/undervolting-in-linux-via-modified-bios/
http://rumorscity.com/2014/01/03/litecoin-mining-sapphire-radeon-r9-280x-sweet-spot-for-740khashsec/
http://forum.feathercoin.com/index.php/topic,7365.0.html
http://forum.feathercoin.com/index.php/topic,6938.0.html