John at NYCNC posted a video yesterday where he is pushing the superfly pretty hard.
https://www.youtube.com/watch?v=PMbjj5qsGp8 go to 9:14 to see the superfly in use.
A multi insert facemill will not be able to remove metal any faster on a 1.5hp machine.
I personally don't push it that hard and use my insert EMs for roughing.