I have a 5830 card that I recently installed but I can't seem to get it to overclock to the degree that I see others doing.  I can only increase the clock speed to 950 MHz where I see several reports on the mining hardware comparison that state 1040.  I haven't tried to mess with the memory clock much I have tried it at the stock 1000 MHz and 810 MHz.  Is there something I'm missing here or is it just a poor performer?

If it matters I am mining with guiminer, phoenix with the phatk kernel that is bundled with guiminer. (-k phatk VECTORS BFI_INT FASTLOOP=true WORKSIZE=128)