Had a bit of a light bulb moment last night, realised I had an old Amazon Fire box in a drawer from a few years ago.
fired it up and set it up for my plex server and bamm really big improvement over the built in app for plex on the smart TV.
Havent had chance to try 4k content yet but on high bitrate full HD it was slick (2hour film with file sixe of 13gb)
One other thing I found out the other day is the wired Ethernet port on the Samsung smart TV is only 100mb and was clipping out running from PLEx which is annoying, I think because the Fire TV has 1gb Ethernet it is much brisker with the plex server.