316/516 + DLNA/PLEX questions

I am looking at purchasing either the ReadyNAS 316 or 516 in the near future, and have some questions about the built in DLNA server versus installing the Plex Media Server.

I understand the difference in horsepower available on the units (atom 2.1 GHz vs I3-3220), and that the 516 comes with twice as much ram onboard.

Is there a list of file types supported by the ReadyDLNA program? I already know what the Plex Media Server supports for file types.

Main purpose for either of the NAS's is to provide backup for 8 computers and provide media streaming to various TV's, computers and tablets. From reading at the Plex support site, the 516 supports video transcoding at 720p and up, whereas the 316 may begin to be underpowered at 720p and up. Is this really a big deal? Does the Plex Media Server have better support than ReadyDLNA?

Any information would be greatly appreciated.

Thanks

Jerry