What machine and spindle do you have? If you have a 2.2kW spindle or router that's probably too fast. I have a 3kW spindle and a comfortable speed for me, albeit a bit conservative, is 175 to 250 if I'm only taking 1/4" depth of cut. Will 1/4" get you past the upcut portion of the bit? You'll need to ensure you go past that.