Over 1,000 rpms, i would use 1500/2000 rpms. The worse damage would be if you hung up the cutting tool and it chipped or loosened the carbide tips which are brazed on the cutter. All the cutter we use on CNC equipment are carbide, it is the best outside of ceramic or diamond inserts which is only used for heat treated materials. You can also run the cutter dry, no coolant on cast iron, on alum use kerosene or diesel fuel to keep the alum from sticking to the cutter.
Zip.