Jeremy
unfortunately there is no way to back-convert TC9 projects to a previous version. Yes, backup or - better yet - versioning of tests in an SCM are recommended options before converting projects, and in fact for any sort of disaster recovery in general.
I am sorry to hear that you have performance issues with TC9. We have uncovered a number of issues and have solutions for almost all of them, please check the following thread:
http://community.smartbear.com/forum/post/?mode=singleThread&thread=2d2828b9-5b66-4b5a-b94a-a739332514c8
If none of those cases match your symptoms, my best suggestion will be to contact our support directly. A number of users reported that in general TC9 is faster than TC8.x unless of course you happen to run into issues described in the thread above.