So to answer the question on what numbers to look for when thinking about machining steels:

The yield strength, the elongation and the ultimate tensile strength and the hardness. The higher these numbers the more of a bugger a material is to machine.

What you need to know is the surface speed that works best for a given material, luckily the suppliers will have a good idea what this is so you can find it in their datasheets.

From the surface speeds you can calculate the various other numbers you need.

Plenty of literature on the web and of course cart loads of reference books with the theory of chipping and all the other stuff. I will send you the title of my reference when I get home.