because a dvd says 4.7GB on it does NOT mean that there are 4700 MB on the disc. there are 1024 bytes in a kb, 1024 kb in an MB, and 1024 mb in a GB. if you do the math you end up with about 4.36 true GB. it's the same with hard drives as well.
DVD-5 is specifically the setting for single layer discs. use this default setting on the opening screen of clonedvd2 if you're burning to single layer discs.