I was surprised to see Plex streaming just fine on my 4 Apple TV 3s, each of them a different movie and all 4 ATV3 on WiFi.
The server is a Mac Mini 4GB ram(only), 2.6Ghz, wired into the router.
I thought I'd share this info just in case anyone is wondering if this is possible.
Thanks Plex devs, just purchased the life membership since I love Plex. I just hope one day Apple will just support Plex full stop and not to have to use all the scripts I do atm. But even so it still worth the hustle for the experience.
Cheers!