jrb -
Couple of things. You can't compare a Mamba to an x-200, different animals. When referring to arrow spines, draw lenght and arrow length have to be included, else the information is meaningless. Also, it's possible to tune several arrows to shoot cleanly out of a given bow. The trick is to find the best arrow in the first place. Not only does it make the tuning easier, but once tuned provides the most efficient (read best performing) combination. A lot of people are more concerned with feeding their egos these days (my bow needs a stiffer, heavier, whatever arrow than everybody elses...) than giving the bow what it really needs.
If your arrow length is 29" or less, tune a 2018 and a 1916 to shoot correctly from your bow and shoot both through a chronograph. The extra 60 grains of weight makes a difference and not in your favor.
BTW - if you get into the penetration arguement, the difference in momentum between a slow moving heavy arrow and a fast moving light(er) arrow will NEVER mean the difference between a successful harvest and a wounded animal. It might however mean the difference between a clean hit and a miss, due to the change in trajectory.
Again, you can shoot or do what ever you like, no real rules. I just like to know I'm getting the most from my equipment.
Viper1 out.