KE is easily calculable. Add 120gr to my current arrow.....chrono it....and there ya go.

Now explain the difference in "momentum" and how that becomes more "optimal" when the KE goes DOWN (which you must know it WILL DO when you add 120 gr of arrow weight). This says nothing to spine issues, either. You're either going to have to add it at the head (FOC AND spine issues?) or in the shaft/fletching area (FOC AND spine issues?).