My dear,
first of all you should get easily 570khash on each maybe 600 with 72C temp (room temp25C) with stable condition =>1 week
1st- get nice cheap professional PSU like delta series for IBM serveres - you can get them under 20 bucks with 1200 SERIOUS WATTAGE capability,(there are 1800 and even 2,5/6/8Kw versions on the market) unscrew it, split and let them breath/cool maybe add some fan... (Im supplying 4X 7970 on 1 = one , 1200db delta ibm)
2nd check voltage and amperage on all pins for your knowledge [and do it always before adding extra power consumption unit]
3rd play with your mem and gpu clocks at least long you did it already with your girl/boy Friend
4tth its really possible to get almost 600khash on 7950 specially if you run cgminer under any debian tree distro.
5th- in need of answers pm me
this are rates for scrypt mining LTC/FTC/CNC etc
7th (don't ask where is 6th) Never trust any PSu , always open it and check main components like trafo, BIG capacitors etc.. I got bunch of shit worth, 1000 watt called psu on stickers. Don't trust stickers
8th adjusting voltage on gpu/MB in my private opinion is pointless. Let me earn some lesson if you are successful with over/under volting
Jep, I´m geting 610kh from my 7950 and 670kh from 7970 even with GUIminer but cause it is not open air rig then the temperature is about 80C. I put the 80mm fan to blow between the gpus.
8th adjusting voltages has point only if you lower them - saving energy.