Lowering transcoding CPU usage

I have a file server and for the most part things work wonderfully with serviio and some things transcode fine. However there are some files that just fail to transcode at a fast enough rate and CPU just sits at 100% and i get stuttering on the TV

Server is older 939 AMD64 4600+ and i fear its probably missing many of the CPU optimizations that are available in current generation processors.

What things can i adjust that decrease the strain?
Reducing target bitrate?
changing target containers/formats?

Or am i better just to sit down take the time and pre-transcode those files that don't play myself so that serviio can serve them direct without transcoding?

[NX3]

Whats your playback device? Would it be easier / best to get a device that plays your files natively so no trancoding needs to take place... ?

I've been messing with the DLNA on my panasonic VT30a (I can't exactly replace it) Also tried the sony BDP S580 interface but thats just clunky compared to the TV.

It plays most things but there are some HD content that is encoded in VC-1 which serviio transcodes since the TV won't open it. (that I have found so far)

I already use an NMT (a very old NMT based on the older sigma chips) the reason i'm moving away from it is that it struggles with high bitrate highdef video.

I'm trying to avoid buying another device because as much as DLNA works it seams to have quirks with everything as such your better off just using a cifs share and using a device that plays it all. The other thing I might just have to do is pre transcode the content that fails.