Zero1, like you know, several people in this thread already commented on the Windows NT process accounting (CPU usage measuring etc.) being inaccurate measuring CPU usage, and as such, it being a completely useless statistic about a codec. I managed to reproduce LytHka's unrealistically low CPU usage on VLC a few times, and then I couldn't reproduce it again.
If you want to measure how effecient two codecs are, you need another measure, namely the "how fast can it decode this clip". Haali created this tool for testing DirectShow codecs:
http://haali.cs.msu.ru/mkv/timeCodec.exe (TheFulff also linked it earlier.)