althor1138 said:it seems that with a bit-rate over 15mb the advantages of x264 drop off.

Yes, but you will still get blocking with MPEG-2, even at high bitrates. If you must make a BD, use x264. You said that you have solved the compatibility issue, and if the encoding time is a problem, drop the bitrate; you already have far more than you need. (At the bitrates you are talking about, you might as well upscale to 720p.)

EDIT: It is also possible to encode in 4:2:2 colorspace.

It is possible to encode it, but for BD stick to 4:2:0.