Answering all the questions:

I am pretty certain that going to a lighter arrow is almost always a small penalty in down range KE, a somewhat larger penalty in penetration, and a benefit in trajectory.

With modern compounds most of us have enough penetration that we can afford to trade some for a flatter trajectory - and we all do, nobody shoots 1200 grain arrows.

IMHO, carbons are a little better than aluminum. For equal weight, equal spine arrows, the smaller O.D. of carbon arrows is an advantage - how big, I don't know.

For penetrating targets, the smaller O.D. of carbons is usually a big advantage. That's the lie that the target is telling - carbons will not have the same advantage on a deer.

I shoot 602 grain arrows out of a 60# bow and have about 53.5 ft-lbs initial KE, or I did until a couple of weeks ago when I twisted a limb. I plan to replace my bow with a 70# bow and shoot heavy enough arrows that I get good flight out of fixed broadheads - probably about 560 grains to keep the speed below 250fps.

beprepn