I used to use 4 flute end mills on woods, like walnut, bambinga, ebony ( watch out for stone in the ebony ), and other harwoods in the mill. I would recomend cobalt over HHS as you will be running at high speeds. You can use the same end mills for Al and brass. Frankly, the carbide router cutters would be better for wood.
I am am sure the gantry / router table guys will chime in with better advice.
RICH