Wowzah! That sounds like something is wrong. I'm mining with a 6850 and a 5850 and I get 650-750kh/s
Where are you located? I'm in Texas and it's hot as hell over here. I've been trying to burn out my 5850 so I can use it as an excuse to get a new card, but it's been running like a champ between 85-90ºC.
If you can stand the noise, you might try to open the case and let the cards breathe and see if that helps control the temps. Or see if pushing the fan to 100% helps.
The only other suggestion would be to get a new motherboard that has more space between the slots. Also, you could get some pcie risers and move the cards farther away from each other. I want to build a custom case but my wife won't let me... lol
Good luck!
Thanks for quick reply mate, I'm in London and it's not too hot. My room is probs around 23-24c. Can't get more than 500kh/s without my PC shutting down because of heat.
If I had the money I would buy a aftermarket cooler for the XFX card, the stock cooler is junk, at idle with crossfire its 59c!. Do you think it would be worth selling the XFX card and using the sapphire for now and buying a different brand like Giga or something?
Already got the side of my case off and a small exhaust fan right by GFX cards.
No point getting new mobo, got the best LGA 775 you can get the ASUS p5q deluxe.