1080p MKV file stutter on PS3 from HP Microsever WHS2011

Running Serviio on a wired network from HP N40L Microserver (8GB Ram), OS is WHS 2011. Trying to play files on PS3.

PS3 can play the smaller files ok, but the larger 1080p MKV files stutter immediately.

Are there settings I can tweak within Serviio to fix this?
- The Playstation 3 profile is being correctly assigned on the status tab
- I've enabled Transcoding and allowed both CPU cores to be used. Also unticked 'produce the best video quality', on the transcoding tab

Or is it a case of the server not being powerful enough / the PS3 a bad choice of playback device when it comes to MKV's?

Thanks