Thank you both for such descriptive answers. I read here that you can have your inverter "tuned" to get lower rpm, but I guess that's wrong then.
Anyway, JAZZCNC, where did you buy your end mills, and do you have any suggestion for good price-performance wise end mills for aluminium?
I guess I will need 6,8,10 mm 2 flute end mills for pocketing and something like 8mm 3-4 flute for inside-hole finish.

Thank you again!