XRECODE

I can split to m4a and get the results i want.. similar size file and bitrate. The size doubles when i go to mp3.. I seem to recall that it could be done easily with xrecode3, but i am not finding it in searches of forums or in my notes.
Perhaps i am not searching correctly here?
Can this be done with a preset, so as not to mess up my settings for normal flac to mp3 conversion, in which i like much higher quality?

You can just add a new tab https://imgur.com/Igewuks and have the audio book specific settings there.
You can also right click in "Output Format" https://imgur.com/3ebVbq4, click Arrange and remove all other unused formats under that tab.