Ok, found the prob. Problem was in activated overdrive by default somehow. Still, its pretty good results with it - max temp 68C with 310 mhashes/s. And I even not yet underclocked mem/undervolted it. Sweet.What OS, Driver, SDK, Miner.... and clocks ?
I can get 310+ MH/s from my Diamond Reference 6870's, but have to run them at 975 Mhs on the GPU clock to accomplish it.
(Win7 x64, CAT 12.1, SDK 2.4, CGMiner 2.3.1, 975 Mhz GPU, 875 Mhs MEM, Stock Voltage
Win7 x64, CAT 12.1, SDK 2.4, phoenix 1.7.4, 960 mhz, sapphire.