I'm trying to follow your hardware and software moves.
It sounds like you want to run OS 9.2 on the G5?
Please note that the G5 will only run OS 10.2.7, and will never be able to "boot" into 9.
It will run "Classic", but thats a very poor use for the G5!
If you want OS 9 then you should keep the G4!
Performance-wise, run your system off the internal drive and use the external drives for apps, data and scratch disk files.
Have fun!
