I believe the Hypertech will let you change the automatic transmission shift points and firmness, while leaving the ignition timing and air / fuel at factory values (you may wish to verify this).
However, I would choose the Predator for more features and versatility. After all, you own a V8 Mustang so I would go after this mild engine performance tuning as well.
I have the Hypertech but I have the 5 speed. It does have the option to change the shift points and the firmness but that is all I can tell you since I have never used that option. It does give you step by step instructions on how to change the shift points if that helps any.