When i did the update i found some good sites that tell you alot of good info about the MkIII. The MKIII got its last update at V23 and then after that it didnt get any updates so from V23-V28 there is no difference but i would get V26 if u can.
Here is a link to the info about V26 and it has download links as well
http://www.xoutpost.com/navigation-sy...-released.html
Info about burning the discs and all the other versions here:
http://www.xoutpost.com/articles/all-...ng-system.html