I use windows so I can't tell you a 100%. As long as your song or project isn't saved in a version of studio one past the one your using, you can't open songs made with S1 5 with version 4, you shouldn't have a problem. The only issue I can think would be caused by Apple and their dislike for backwards compatibility. So if you want to stay with Version 4, just stay with it until Apple won't let it run. S1 5 can open 4's projects, so if you need to update later on it shouldn't be a big deal. Until then just keep 4.
