OSX is not faster than OS9 although but it is also not much slower. I would expect the final release to be faster than OS9. If it isn't the adoption of it will be slowed as many users simply want speed more than anything else.
I've used the beta and when I removed it there were still hidden folders on my OS9 partition. They appeared when I ran Norton on OS9 and I couldn't get rid of them so I just reformatted and reinstalled OS9.
The documentation that is on the OS X site says that you will need a bootable CD so that you can select OS 9 to restart. If you are running only the Beta than you are pretty muh SOL.