Aluminium FEA optimalized CNC router

[remrendes]

Requirements
Speed: standard 0-2000mm/min max 3000mm/min
RPM needed:
5mm lead; standard 0-400RPM, max 600RPM
10mm lead; standard 0-200RPM, max 300RPM

A stepper motor seems to lose it torque from 300-500RPM
A standard servo motor has full torque up to 3000RPM. However to utilize the whole range I would need a 10:1 or a 5:1 reduction.

If you buy a not Chinese stepper, probably it is higher, like the price :) But yes, you should calculate up to 500rpm.
With 5mm lead from 2:1 to 3:1 usually enough with servos. On 2.5:1 ratio I can get up 6000mm/s no-load speed on 3000rpm. But some motors could do 4000rpm.