@scarr I too struggle to really understand it. My solve is that every time I purchase a new bot and do not have a point of reference, I post the purchase in the forum, the wood type I plan to mill, along with the screenshot of the feeds and speeds I have selected and then I will usually get a response within 24 hours
Example:
The other thing I like to do is troll what others have purchased. One of my best purchases was suggested by @fenrus . That way I know that they will have a good direction for me in terms of F&S
Always make sure to tell them the machine and router because that he has to be taken into account