I've been running Plex since it first came out and it's great. I tend to find that my N40L is on the cusp of being able to transcode HD content. Generally I find that 720p is doable as long as the machine isn't doing anything else. 1080p is a no-go. SD content is no problem at all for mine
(For info I'm running 8gb Ram and Windows server 2012 Standard)
(For info I'm running 8gb Ram and Windows server 2012 Standard)