The best setup is explained here:

http://customscreatorscollective.wordpr … 03/29/155/

You can keep TU5 so that you can buy new songs (do buy new songs from Harmonix and RBN authors, they deserve the love) and you can get TU4 for all the content.

I don’t think it’s specified in our video, but I always recommend creating a new gamer’s account with no Live connection for TU4, so you won’t be bothered with TU5 upgrades requests and your offline scores never get posted.