I recently ran across an interesting broadhead test. https://docs.google.com/spreadsheet/ccc?key=0AgJEvQwzfDRZdGxzdC15R0JIZDJGQ1J4bVpGV1pTWHc#gid=0  If you look at the spreadsheet you can see the fixed heads dominated the test.  It was basically a test about penetration.  Using a 60 KE setup each head was shot into a “contraption” that consisted of plywood wrapped in vinyl, ballistics gel, and another piece of plywood wrapped in vinyl.  It was meant to simulate a shoulder hit.  In my opinion most people use around 60 KE.  If you want to use mechancials I would suggest at least 80 KE.  I think that is the biggest problem most people have with mechanicals they don’t use enough KE to get that pass through 100% of the time.  Without that exit hole your odds go way down in finding your game but thats another topic.