I had SD24 on mine and recently updated to SD28 because I didn't realize they did frequesnt updates and don't really notice any changes in performance in normal tasks.
The latest one obviously, the people who brought you SD25, aren't going to magically mess SD28 up.
I don't understand people who refuse to upgrade their firmware, usually they're the same ones who complain that a company doesn't support its product after release.
You should only upgrade the firmware if you have problems.
I had SD22 without problems, and bugged it up by installing SD23 just to be up to date.