Basically

High RPM for aluminum (light feed load), slow for steel (heavy feed load), very slow for stainless steel (with very heavy feed load). Boelube for aluminum, any oil for steel, and specialty cutting lube by Castrol called Moly-Dee for 4130 and SS.

There are more specific recommendations out there I'm sure, but the above has worked well for me...:)
 
fly cutter and AL: slowest possible speed.
I found that unitbits also work well on AL at a slow speed.