What's the best brand for 5970 in terms of overclocking/Mhps?
I got my Gigabyte 5870 to 450Mbps without much sweat, which is quite high for a 5870.
But my Gigabyte 5970s can't seem to go post 700Mhps without freezing the whole system :/
I'm running them at 180/800MHz/Default voltage
Mbps? You mean MH/s?
I kid...
It's really card dependent. I like PowerColor, Sapphire, and Asus. A lot of people have good luck with Gigabyte. I've heard to stay away from XFX and Diamond, but again, YMMV. There is no BEST brand for OCing.
Also, while a 5970 is technically 2x 5870s in one card, the voltages are lower to keep the power/temps down. Stock voltage on a 5870 is 1.174, while stock voltage on a 5970 is 1.050. If you lowered your 5870 down to 1.05, you won't be getting 450MH/s.
If you raised your 5970 to 1.174, you MIGHT be able to get 400+ per core, but it would be a very bad idea. Power draw increases, temps become too much for the shared cooler, and your VRM temps would be through the roof. Not a good idea.
Side note: Here are my 5870 speeds, for undervolting comparison:
460MH/s - 980/300/1.174 - My "all out" setting
425MH/s - 925/300/1.000 - My "max profit" setting
350MH/s - 755/300/0.950 - My "keep the temps down" setting.
I think my card can get higher clocks at each voltages than average, so yours may be a little lower.
you should try higher at 0.950v... mine has been stable for 200+ hrs at 830/195/0.950
the next step for me is 940/195/1.112
then 1010/195/1.175
it's xfx non-ref (hmm or maybe a sapphire non-ref... haha)