Coming up with optimum codecs is a never-ending challenge.
I use Apple Compressor, as part of Final Cut Studio, but Compressor is also available as a standalone for only about $50 (Free 30-day Trial too).
Apple Compressor specs/ordering
I had to tweak it quite a bit, and came up with a few workarounds to avoid having to use some of the pre-sets, and still I'm customizing my codecs to try and find the right balance between file size, speed, and quality.
I am creating 1500kbps as my middle setting (Hi-Med-Low), to stream h.264 mp4 files. (4000kbps is high, 750k is low)
Good luck...
ADG