re: If I replace my iPhone 5 w/a 5S purchased in full, will my current contract end date stay the Same?
It would stay the same if you just swap phones.
I just did the same thing last night. Back to iOS 6.1.4. Loved iOS 7 and can't wait for beta 2 or 3. Battery life just needs to be a little more stable but I love where Apple is going.