Okay, I was off on that apparently... Higher intitial momentum must keep the speed up above that of the lighter arrow with lower initial momentum - even though gravity is playing a larger role with the heavier arrow.

Thus, KE isn't a good gauge. Momentum (even intial momentum at release) seems to be a better gauge for hunting/penetration purposes than KE... Why bother calculating KE and not use momentum? The energy in the arrow at release is not a real good gauge. I'd rather calculate momentum and know that the higher initial momentum will penetrate better at any range. The other key factor is that your bow efficiency will most definitely increase with a heavier arrow - more potential energy transferred into KE and less lost potential energy.