Eh, I'd still go with Tiger. I know the OP's PowerBook is faster then my old 1.33 GHz iBook G4, but when I ran Leopard on that thing even with maxed out RAM, it just wasn't satisfactory.
How much RAM did you have, maxed out? His PB also has a slightly faster system bus than your iBook, but I can say that on my PowerMac G4 (see sig for details) even with a slower CPU and system bus I cannot see any performance difference between Tiger and Leopard.
There is one reason to choose Tiger over Leopard, and that is if you need to run Classic mode for anything.