I realize that OPENSTEP isn't quite OS X... but what would it feel like to be running OPENSTEP proper on a 2.5GHz processor (when it runs nice and spiffy on a 100MHz processor).
Now there's an idea for a swell hack!! Install and run x86 OpenStep on a new MacIntel! How freakin' cool would that be!??! Near useless, but really freakin' cool!