I must declare it isn't "overencoded from 128k". I used 320k mp3 and use default options in liblamemp3 to compress, and due to the special instruments in this song, the highbitrate was automatically cut-off and in spek or other visualization program it looks like a 128k audio file.
That's a reason that even you choose ogg vorbis q6 you can still get bitrate higher than 208k. And when you choose q5 you should get a similar quality as the current mp3 file.