that's probably a silly question. OS X is a "next generation" operating system and honestly needs a lot of processing power, fast hard drives and RAM up the zazoo, though they all depend heavily on what your tasks are.
OS 9 is a real piece of work, somewhat like windows 95... it will be blazing on your ibook.
i use an overclocked dual usb ibook as my main computer with 576mB of ram. i wish it would take more ram, i wish it was faster and i wish the hard drive wasn't so lousy. but it gets the job done and is sufficient that i don't run out for a new machine just yet.
OS 9 will be faster. OS X will change your world. you decide =)