You don't say what computer you're running it on, which makes a difference. By the time you get to 10.4, there are a lot of Power PC - specific extensions and such baked into the OS. Unless you have and use the original installer, you need to optimize the OS for your particular machine.
That all said, there shouldn't be a big difference in the apparent "speed" most or even all of the time…unless you don't have enough RAM or a very slow HDD or a fragmented-from-poor-housekeeping HDD or……?
A reply with your machine specifics and more detail in general would be helpful.