Use PVD coated micro grain inserts,with sharp edges,try to avoid 95 degree lead angles.
I'm an expert on super alloy machining.
Look into turning (finishing) with PCD diamand tipped inserts,if you feel like it talk to Seco Tools.
Try an octomill 05 face mill from Seco Tools(carboloy in the States).Use a PVD coated micro grain e.g.F40m in an easy cutting geometrie,with the small depth of cut you can use a higher cutting speed than normal and use lots of coolant.
What works very goed on these types of materials including...
If you have trouble with low revs that result in low cutting speeds,try if possible to use larger diameters of cutters.With the adding of a high speed spindle you dont solve the problem really,if your machine is not able to accelerate and diccelerate and run at the programmed feed rates you...