RE: weight of broadhead
There are multiple ways to accomplish the end result, but the most important thing to pay attention to is your FOC. Keep it at a minimum of 12% to 15% for broadheads.
I have some FMJ's that I built with 100 grain brass inserts to achieve over 20% FOC with a Slick Trick 125 grain mag. The extreme FOC arrows really perform awesome!
Dan