This problem crops up a lot with trying to stream mkv files wirelessly. PMS has to transcode/remux the file so that the PS3 can play it as it does not support mkv files. As soon as you have to do that you will see the buffer on PMS filling up, well you should with 4Ghz to play with. The wifi part of your network is now a bottle neck, it will not be able to transmit the dta fast enough to prevent stuttering, the transcoded data is uncompressed, an mp4 stream which the PS3 does support, is streamed compressed so uses far less bandwidth. You can try and adjust some of the Transcode Settings, Common Transcode Settings by adjusting the maximum bandwidth setting, reducing to 15 and lower if you need to and by changing the MPEG2 Video Quality settings to keyint=25:vqmax=5:vqmin=2. This seems to work kinda well.