Probably … 5.3 is “better” in any case, than 5.0.2 which I assume you are keeping (as I did for a long time) for Plex. The problem also is that the Apple TV Plex plugin is no longer being developed and will sooner or later stop working. You’ll need to go with PlexConnect (and OpenPlex which makes the whole process really easy) if you want to keep using Plex on your AppleTV. PlexConnect or OpenPlex do not require a jailbreak. So, if thats all you were using it for, you could go all the way to the latest for the AppleTV and get the most recent aTV apps as well.
If you want to use Infuse instead of Plex, 5.3 is the one you need. You’ll need to use the latest Seasonpass and let it jailbreak on 5.3. It ought to work. Otherwise, hit the Plex forums for the links to install openplex or plexconnect on your computer. (A word to the wise: Because of how this method works, via Hijack of the Trailers app… if you dont want to lose that - I didnt - you can only make a different choice between trailers, imovie and wsj if you use OpenPlex. You’ll find info about that in the plexconnect subforum)