Nah I doubt it's his PSU. I could OC when I had a Sapphire using a cheap little HP 350W PSU.
BTW I wouldn't worry much about the GPU frequency. Focus on getting that memory up there. You memory is rated at 1.2ns, which is a nominal freq. of 800 Mhz . I know people clocking the Sapphires up to 850 MHz. The highest I have gotten mine without artifacts is 823.5.
Also, if you have FEAR I would use that grahics performance test to see where your diminishing returns are on your OCs. TBH I don't remember a difference in the core clocking much...but the memory was. I read that the card is memory bandwidth limited.
Here is a good thread at techpowerup. Most of the vendors are here:
And Grunion I loled at your sig! Nice!
Also, how is the image quality on those DNA drivers? I've never tried them.