i think your problem is not the spindle speed, its the feed and depth..
try this option since i am doing tool steel as well on my current job..and it works good, i dont have the same cutter as you, but i think should be close enuf..
try:
2mil depth of cut (inch 0.078 i think)
spindle speed 1273 rpm
feed 4 to max 5 inches per min...
and dont use coolant what so ever..not even a drop or mist..
you can blast dry air would be heaps better...
hope this helps