Sympathise. I’ve been trying to wrap my mind around this sort of thing for a while now.
Suggest starting with the official recommendations: http://docs.carbide3d.com/support/#tooling-support and http://docs.carbide3d.com/support/supportfiles/S3_feeds_250.jpg
Then look into using the testing technique here: http://www.precisebits.com/tutorials/calibrating_feeds_n_speeds.htm
Been trying to work up a tutorial here: Tutorial on feeds and speeds but it’s nowhere near complete. There are a bunch of additional notes at: https://www.shapeoko.com/wiki/index.php/Materials which may be of help, or may just be confusing noise.