It's going to come down to the stiffness of your machine. I have a weak Z axis so I can only take cuts of about 50 ipm at a .07 depth. That's on the sad side but I'm happy. Any deeper and I end with bad edges. Others can do it at 125 ipm and in 2 passes. I think the best formula for your tool life is going to be the deepest you can go at the lowest RPM and fastest IPM. The bigger the MDF particles you create the longer your tool will stay sharp. Bigger particles will take more heat with them keeping your tooling sharp. Too low of a feed rate and your just dulling your endmill because of all the friction. That's how I understand it.