I recently just milled some custom parts of out a 1" thick block of 6061 aluminum. The AR8 I have worked like a charm.
The absolute key to proper milling of metals is chip/heat removal so that the workpiece and endmill stay cool enough. If either becomes too hot, you will weld the endmill to the workpiece - likely ruining both at the same time. If you allow the chips to build up in the cutting area (so that they are re-cut), overheating will quickly occur.
You can avoid this by paying attention to two things:
1) Use an endmill with no more than 2 flutes. I use the single-flute aluminum but that axiom sells from Amana. Fewer flutes means larger chips - larger chips are more easily evacuated from the cutting area, which means less recutting - reducing heat and improving tool life.
2) Promptly remove chips from the cutting area. Using a standard dust collection system and the Axiom dust shoe, my cuts had no problem staying clear of chips - even in nearly 1" deep pockets.
If you're not sure about your feeds and speeds, one product I can't recommend enough is "GWizard" (I am not affiliated with it in any way - just crazy happy with the product). I used my CNC mill for nearly 2 years before I decided to try it and - holy crap!
It's a software that tells you what your feeds and speeds should be for different endmills in different materials and I had no idea how much better I could be cutting until I tried it. It was absolutely instrumental in making my aluminum cuts nice and smooth. They have a one-month free trial that you can use to check it out. I just purchased the lifetime license after my free month expired.
As a final recommendation, you may be tempted to have a deep depth of cut and a narrow stepover (as is typical in adaptive clearing paths so that you use more of your endmills cutting surface instead of just the tip). However, you'll likely experience some chatter if you're using a narrow endmill (1/4" or less). If that's the case, go with a shallow depth of cut and a wide stepover. You'll only be using the tip of the endmill, but you'll get a lot less deflection and a much smoother cut.