Like I said, you aren't going to get smaller files without making a sacrifice. If less filsize is most important to you then you should focus on a target bitrate at the expensive of quality.
One option is to requantize original MPEG2 stream.
http://code.flexion.org/M2VRequantiser.html
It makes your file smaller with minimal quality loss on video 'focus' area. But it is fairly fast and easy to use via pipes. Demux -> requant -> Remux.