5.4 gb is pretty huge. Usually that comes from restoring from backup of the course of many years/phones/updates. If I were you I would sync my contacts to iCloud, back up photos on the computer and restore as a new device.
FYI, found the main culprit in my file size. I noticed that a couple songs would not play on my iPhone but would on my PC. I trashed all the music from my iPhone and reloaded. My "Other" went from 5.4 GB to 1.5. Edit: Still can't play all the protected AAC songs. They worked before the iO6 upgrade.