Just to expand apon what he said:
Stuttering/jerking is usually caused by the CPU being unable to handle the load. (*Resolutions > 480)
IF on the other hand it was having to constantly rebuffer your movie that would be a likely issue due to the WIFI.
(*To be absolutely clear, by “rebuffer” I mean playback stops and the normal buffering % counter appears)
Usually it takes 4-6+gigbyte files to actually max out the WIFI.
(I’ve pulled it off since my collection is based off transcoded MPEG2 dvd->MKV)
If you are convinced it’s a WIFI issue you can always test it yourself by loading the file locally to a SD, USB Flash, or USB Harddive. You will need USB2 support loaded via ISO58 to be sure.