For a well tuned arrow, I think there is almost complete agreement that a heavier arrow leaves the bow with a little more KE and keeps a little more of that KE down range - think of throwing a golf ball and throwing a ping pong ball.

For penetration, I think (with apologies) I have shown, KE is sometimes the correct predictor of penetration and sometimes momentum is the correct predictor (all other things equal), but even for the cases where KE is the correct variable to use for predicting penetration, the heavier arrow wins as it will also have a little more KE based on the above.

But, we all know that accuracy is crucial, and for our rainbow trajectory weapons, fast arrows are a little more forgiving of range estimation errors.

Some say that beyond 250 fps fixed blade broadheads may plane off line.

Given all this, my personal decision is to use 500 grain arrows for my 60# bow which gives me about 250 fps and a decent load of momentum.