You will need I think 50 # of KE for mech. to work properly. There are an infinite amount of combinations to try, but a good rule of thumb is 6 gpp. I shoot 5.6 gpp, and this works very well with my set up. The key is to get the most speed with the heaviest arrow combination. Remember, a 450 gr arrow going a little slower than a 400 gr arrow may give you more kinetic energy and momentum, so you gotta get the combination right. Also remember, that the lighter the arrow, you will get a little more noise at the shot. Start at 6 gpp and go from there.