I just uploaded version 3.3.36 which now supports this. The mod finds belts in the game prototype table and uses the belt_speed values from there, rather than being hardcoded. Belts from theFactorio Extended Plus Tranport mod show up now in the drop down and seem to have appropriate values.
I looked into doing the same for inserters, but the inserter throughputs I'm currently using are based on data in the wiki. Their speeds are dependent on animation speeds, and I can't figure out how to reconcile those speeds.