Having pre-rendered clips in the XPression codec have helped us tons with performance issues. Instead of trying to do flying text on top of an alpha tracked video with other elements thrown in, just rendering it to a single file and using that as a material on an object works.
There may be more and better ways of doing it if that's not possible for you, but anytime we've been able to take the render portion of the work off XPression, it works better.
#XPression