Note that if it is a copyright book, you will want to scramble it first. Helps keep the greenies (moderators) happy. BTW, the calibre plugin (
[GUI Plugin] ScrambleEbook: Getting help with copyrighted books ) works with epub/kepub and azw3.
Personally, I would remove the .mobi copy unless you have an old device that needs that format.
Edit, you know I should learned that always read to the end of a thread before replying is a great idea.