Just to clarify in case you don't know, the memory is DDR (double data rate) so your 297 Mhz is really the equivalent of 600 Mhz... or that's how they advertise it anyway.
Still, if it's advertised at 640 Mhz then you should be running about 320 Mhz.
It's weird that they would advertise it at 640 though, because the 9600 PRO spec is 300 Mhz DDR (600 Mhz effective).
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Radeon 9500 (modded to PRO w/8 pixel pipelines)
AMD AthlonXP 2000+
3dMark03: 3529