Chris, I'm not a pro machinist, so I just go by how it sounds, and my mini-mill doesn't have an actual RPM speed chart, though I bought an optional tach that I never hooked up. I am guessing I run about somewhere between 1,250 to 1,800 RPM, using a 1/2" diameter sq. end mill. I rough cut sheets of aluminum with a saw, then clean and square the edges with the mill. Sometimes the smaller pieces can be clamped, on edge, in the work vise, but if the edge you are cleaning up is not well supported, it will flex and vibrate, and that doesn't do the end mill or the piece any good. More so on the thinner material, obviously. It depends how much hangs outside the vise jaws, and how thin the sheet is. All of my end mills are just high speed steel, coated with TiN. I also run some oil, applied manually with a bottle.
Kind of low buck operation!