Get a Daystar
xlr8yourmac's Mike Breeden is selling one of his two Daystar Genesis systems with some very appealing specs. Keep in mind these machines used to be the best (and I mean the BEST) that you could get for several years. Also it's most certainly the most expandable Mac there ever was.
MacNN's forums are again sporting some interesting threads you might want to read:
MP G4/533 vs SP G4/733
FireWire HDs inside G4's with internal FW port