Personal best on this 5830 is stable at
320 Mhash/s
still 2.1 SDK
phoenix+poclbm
1025/320
90%
Still need to play with phatk, overvolt, flexible proxy miner, etc. Fun little toy project

Card will in theory try to go up to 1200 GPU core, so I'd imagine I might in theory be able to get up to what... 350? I don't think I can do that with stock cooler and volts though.
How are you OCing the core above 875 in linux? aticonfig is limited for me.