I also have an xfx 5830 and after seeing this thread switched from puddinpop's miner to phoenix 1.4 (see details below). At a core clock of 970MHz I saw an increase from ~220 MHash/s to ~285 MHash/s.

OS Windows 7 64bit
Catalyst driver: 11.4
Stream version 2.4 (presumably - it's whatever comes with the 11.4 drivers. Anything less won't work for me, at all)
Core clock 970Mhz (somewhere between here and 1000Mhz things get unstable)
Mem clock 560Mhz (can't set it any lower in MSI Afterburner)
voltage is default (unable to change?)

Miner Phoenix 1.4 -k poclbm device=0 platform=1 WORKSIZE=128 AGGRESSION=12 BFI_INT VECTORS

Any suggestions for getting it higher? I seem to be stuck with stream SDK 2.4 and can't raise the core clock much more. For reference, I'm also running a nvidia 260 in the same computer.