G3 Lombard w/ powerlogix G4 upgrade? Options

[Nonz]

I'm about to purchase a laptop for performing (running Reaktor, Ableton Live, etc.). I would like to get a new TiBook 667 but I've been told the old powerbook G3 'Lombard' was better for audio DSP because of the 1MB cache as opposed to the TiB's 256k cache . I found a 400mhz G3 Lombard for $800 and I can get the Powerlogix 500mhz G4 w/ 1MB cache upgrade for it for $500. Anybody use this kind of set up? What should I do?