Most suitable Mac OS X version for Power Mac G5? I have a Power Mac G5 Dual 1.8 with 3.5GB of ram running 10.5.8

The system feels so slow though.. :(

Taking in mind that this was a beast back then, which would be the best OS X version I could install on it, in order to make it breathe again?
You may want to give Mac OS X 10.4.11 a try.

Reference: http://lowendmac.com/ed/royal/08sr/tiger-or-leopard.html