Panasonic Viera and MP4

[06blade]

I have a Panasonic Viera TV, model TX-P50V20B which I purchased in 2010. I've experimented with the 2009 profile and also the 2011 profile.
Using the 2009 profile the TV struggles to stream most formats. With the 2011 profile it seems to play most formats ok, but struggles with high-def MP4's (BluRay rips, 1080p supposedly) - the picture stutters and is very glitchy.

suspecting it may be a wireless bandwidth issue I connected the TV with a wired gigabit connection - still same issue. I've then experimented with changing the Video Bitrate settings in the Performance Tab, again struggling.

In order to try and get the MP4 files to play I've turned on transcoding -
on the fly transcoding doesn't work well - I'm using an HP Microserver to store the media and the processors are 100% CPU during the process
pre transcoding works, but the quality isn't the best - it's actually very poor

Nothing is wrong with the files I'm trying to stream, as it plays perfectly well on a Sony Bravia TV I purchased in 2012.

Can anyone suggest anything else I can try before I spend £60 on a WD TV ?