Material removal rate (MMR) = Power (HP) X K-factor (cubic inches / HP). 1 horsepower (HP) = 745.7 Watts (W). (Unlike the US, most of the world uses Watts for mechanical power as well as electrical power.) There’s K-factors for a variety of materials on worksheets in the SFPF Calculator Excel workbook.
Both GWizard and HSMAdvisor speeds and feeds calculators can use torque/speed curves to keep cutting recommendations within spindle power/torque limitations. HSMAdvisor now can also use machine force limits, which generally is at lot more useful for CNC routers. GWizard doesn’t even display cutting force.