Speed has little to do with recommendations for mechanicals except for it's relativity it plays in KE. ..... in the beginning year of mechanical heads, 55 ft lbs was the recommended KE for use of mechanical heads. Now times have changed and I can tell ya that I use (as a once anti-mechanical) Rocky Mountain Snypers (same as Rage) and they are amazing when it comes to opening on all materials I tested. I first tried them because of a test done by our own 5shot and his broadhead testing page. http://www.broadheadtests.com

My own experience with Snypers is they will open on paper and leave one hell of a huge entrance hole....

HOWEVER, I would not recommend them out of a 47 lb bow. The KE relative behind a bow of 47 lbs would be marginal at best for mechanicals. There is no reason that a person could not get a good chisel/cut to tip/fixed blade head to fly perfect with no need for a mechanical at the lower speeds/lower KE of a 47 lb bow. IMO