If you are really interested in learning about how to set feeds and speeds yourself from scratch, before using a calculator (any of them), I would suggest learning more about the underlying principles of milling. Even though it’s a pretty deep rabbit hole it’s also a fascinating one. There are many threads about this, and folks here who know this topic inside and out and much better than I do, but since I went through the same phase of being puzzled about why on earth GWizard would give me such a wide range of values for a given situation, I took a dive in this topic and tried to document it for the casual hobbyist here. It has a Shapeoko bias on the recommended values, so take those with a grain of salt, but I think all the principles apply as is. Spoiler alert: I have not launched GWizard since then. Not saying it’s bad, it’s just not for me and the turtle/hare slider drove me crazy.
Sorry for chiming in, couldn’t resist, I’ll leave you guys to continue the discussion!