The performance from inexpensive RAM is the same as it is from expensive RAM, basically. Lower 'latency' figures mean more responsive RAM or course, and better performance. But you can get CAS 2.5 to CAS 3.0 RAM in budget lines so go for that. Choose a reputable brand like Kingston, Kingmax, Corsair or Geil and purchase their budget line. Unless, of course, you plan to do some heavy overclocking. That's where the benefit of expensive, high performance RAM comes into the equation. It's not needed for normal use.
Good luck getting hold of an ATi X800XT PE. Far as I'm concerned that card doesn't exist, because just about the only copies ever distributed went to hardware reviewers

ATi will soon be releasing the X850XT PE, which they claim will be easier to produce and put in customer's hands, but it'll only be a PCI card and it'll be more expensive than any other gaming card, EVER!
The 6800 Ultra is a bit more obtainable, just as good, and with SLI beginning to become popular as a purchase option, I reckon the good NVidia cards will hold their value a bit better