With the help of my Sony Rep, I recently upgraded my 6-EX1r's to the latest firmware version 1.15 and had some interesting changes. First of all, it was nice to have them all on the same version as all of them now have the same menu options. Second, the set prefix now appears to be UNLIMITED characters and includes alphabetical, numerical and some symbols. I say appears because it has not stopped me from entering characters up to about 15. I am sure there is a limit but that is plenty for my purposes. This is a great change for me as four was just not enough. It seems in my initial tests that these characters are also accepted in Final Cut Server and Final Cut Pro.
I have had no problems with my 32GB SDHC cards although I did not have any problems before. Interestingly the record time on the cards has gone from 117 minutes on an empty card to 113 minutes. I do not have 32GB SxS cards so I was not able to test those. My Sony rep said he would check on this anomaly for me. I can live without the 8 minutes but would rather not.
So...my initial experience with the upgrade was positive. It was easy to do and beneficial.