the power argument is meaningless... 1 P4 at 3ghz can do the work of at least 4 G3's@600mhz... so one P4 would be more economical... and also cheaper by far...
@mips_proc,
If you're using it as a web or mail server, that P4 is going to be on as much as the G3/G4 system, so the performance increase is not that critical. Granted, if you're running a rendering farm, the extra performance of a 3Ghz P4 over a 700Mhz G4 is going to favor the P4, but I'd suggest that both render farms will still be running 24-hours a day.
The second argument is that, because of the lower power consumption, there's also less heat generated, meaning you can pack more of these into the same space without having a melt-down. If you've got limited space, this might be of interest. The over-all speed is only one factor in the argument.
Zoltan
