For a MkIII the latest is 3-1/63. Any disk V22 or higher will take your nav drive to that revision level.
As for which files to burn, you'll need at least one and perhaps 2. If you are on V17 (3-1/30) or lower then you'll need the KeyCD in addition to one of the disks that is V22 or higher.
Note that you don't just burn the download file to a CD. That is an image file that a program uses to make an exact replica of the original CD.
