Don't assume the Leopard will magically speed up your Mac. It might slow it down, depending on what apps you use most often for long periods of time. Hopefully, as apps are tweaked to take full advantage of Leopard, the potential performance gains will be realized.
Apple has been accused of using Mac consumers as unwitting beta testers. Judging from all the reports of Leopard problems and incompatibilities, that theory has new support.
FYI, there is a recent firmware update for the Radoen X1900 XT. We experienced no performance gains after the update.
More tests are coming. They will include checking for gains after upgrading G4 and G5 Power Macs. We also plan to test additional applications.