Have you tried setting Emby to use another video player for movie files, like MPC-HC? That may fix your issue. This setting is in the Emby Classic configurator, external players tab.I talked to my wife about it last night, and she mentioned that she had gotten so sick of the stuttering while playing through emby that she went and opened the files directly through windows explorer off of the server and still got stuttering. I had assumed that was not the case originally.
So, it seems to either be a local performance issue, a network bandwidth issue, or something is clogging up the file server. Time to get testing I suppose, but it doesn't seem as related to emby as I originally thought.
You can also check the Emby logs to see what it is doing with the file (i.e. transcoding, etc.).