I just setup Radeon HD 5830 card to mine for me and I'm using MSI Afterburner to overclock it.
What's the best set up ?
It's acting pretty strange now, as it is jumping from ~700 khash/s , to around 400 khas/s, ~600 khash/s and then to ~100s Mhash/s    
Im using GUIminer, and here comes the question as well , as im not sure if i have choosen the right options  ( server, device, CPU Affinity, Extra Flags)

Any help appreciated!