I will add that if your main priority is efficiency, you will want to look at @gmack’s worksheet that computes material removal rate, power requirement, and deflection as a function of your cutting parameters, so this should help a lot figuring out how far you can push things on your Shapeoko and/or compare sets of feeds and speeds. It might look a bit intimidating at first, but once you have filled in the static data for your setup (once), and figured out what the few critical cells are, it’s quite easy to use.
I have attached one version in the ebook (here) along with a few basic notes, but if you want to use the latest version it’s available in this thread.