You'll need to pump more volts if you want to get more out of it.. I suppose PCI-E should have stuff like PCI-E volts etc no?
if money isnt an issue, try getting a Zalman VF700 + memory sinks, that should get your temps lowered and possibly a tad more from ur mem chips..
530MHz seems about right.. sad but you actually went for the 512MB version that runs only typical DDR chips.. If you got the 256MB DDR2 version, you probably could have gotten an extra 200MHz more ... and possibly rival something like a 6600GT.
3427 MHz is pretty respectable.. Again, its a pity u actually went for the 512MB version.. I don't think 6600's fillrate will ever saturate that 512MB... not even 256MB
tbh..
Happy clocking..