You could run supercharged spindle speeds if you had a way to keep the thing cool. An air blast would be a good start but you really need to get some lubricant to it. With flood coolant you could run whatever RPM you wanted so long as the machine had the power to push it, but that's if getting the chips out and keeping the cut cool.
If running without coolant, we usually don't exceed 200 feet/minute for an automated machine, so for a 0.125" endmill that's around 6200-RPM, and that's with a standard-length endmill. It would take forever to machine your entire part at that speed