Good advice by by my tag team partner, signals...
I don't like to go much below 80% on movies either. For TV series episodes, you can compress pretty darn far and be ok...it's TV right?
I once did a bkup of T2 down to 52 % as an experiment for another user. Darned if it didn't look and play great on a 32" screen...I wouldn't make a habit of this though...
