Hi,
my calculation was for STEEL....not aluminum. And I based it on a target surface speed of 100m/min which is about right for uncoated carbide in steel and maybe 150m/min for coated carbide.
Plenty of people push that out to 200m/min trying to save time but being harder on tools.
With aluminum surface speeds can be anywhere from 250m/min to 500m/in, so about 2.5 to 5 times what I calculated for steel and if cycle time is more important than tool life you can push it more.
The problem that OP faces is that these spindles have low torque and that's not a good recipie for big diameter tools.
Craig