What is a good "stress test" for a G4?

[TheTominator]

Exporting DV footage (e.g. iMovie) to MP4 with the H.264 codec is pretty darned taxing. QuickTime will use both processors to do it. You should see a performance difference between the two machines there by timing the activity.

You can get a similar test using the "Convert Selection to iPod" in the Advanced menu of iTunes 7 using an arbitrary (non iPod-ready) movie file.