I upgraded my B&W with the fastest G3 processor I could find (1.1GHz). Why? Because it would bug me if I had stuck a G4 in there when the tower says "G3" on the side. 
I only run Mac OS 9 on it so I don't think it would benefit much from a G4 anyway. Plus, for my G4 needs I have a Dual 1GHz Quicksilver. On that I dual boot Tiger and OS 9. Makes a great bridge from Intel Macs to the vintage Mac OS 9 and earlier Macs.
I only run Mac OS 9 on it so I don't think it would benefit much from a G4 anyway. Plus, for my G4 needs I have a Dual 1GHz Quicksilver. On that I dual boot Tiger and OS 9. Makes a great bridge from Intel Macs to the vintage Mac OS 9 and earlier Macs.