MeGUI?
And what is the source? if mpeg2 dvd or bluray is fine,
But if the source video you want to re-encode is mkv(yeah, i know its h264 blabla) fansub,
dont waste your time to reencode them again, cause reencoding = quality reduction, even if the encoder is x264 with Hi10P support.
Some more x264 Hi10P encoding speed is much slower than normal 8bit x264.

You should read this: Generation Loss http://en.wikipedia.org/wiki/Generation_loss
Unless you dont mind about quality or the fansub is too large.

Oh my, good luck with the transcoding lol
CPU transcoding still slow as snail anyway. Hi10P aka 10bit is even slower.
You should try MeGUI as i said, but replace the x264 executable with the one with Hi10P support.