I really don't want to get into this..but I can't keep my big trap shut.. But I will keep it short and sweet. (yeah..right!)

IMO, Momentum should be emphasized (and is KEY) in 2 set-ups

1) where energy (however you want define it) is low i.e. many traditional set-ups, low poundage, shorter draw lengths softer cams/wheels, etc. In those cases, I believe Momentum is much more critical. You want a pretty heavy shaft and fixed blades of some sort to maximize energy and penetration down-range.

2) BIG and/or "dangerous" Game. i.e. Moose, Buffs, the bigger African/Asian/Australian game species, etc. Where you need every bit of "leverage" you can get.

Though we hear tales of the lady pulling 36 pounds who has a 24" draw on an old round wheel bow who shot completey through a Moose with a a 2 inch cut 5 blade mech, I think in those cases, there was a lot of luck invoved and exceedingly good shot placement...neither of which we can always guarantee due to circumstances beyon our control. It's best to plan for the worst..not the best.

On most modern bows shooting fairly light to medium weight arrows at very good speeds, tipped with a stout broadhead of whatever make you prefer, KE is an acceptable benchmark, and momentum becomes less critical unless you are shooting very long bowhunting ranges (i.e. 40-60 yards) for something like Elk, Caribou, big Canadian whitetails, Big muleys, etc where that arrow is coming back into orbit and losing alot of energy.

On deer sized game I feel the point of whether KE or momentum is more important is a moot one. Except in scenario 1 above.

From my experience shaft diameter does provide an advantage in penetration (as well as windrift and less velocity decay) compared to the larger diameter alums with similar (or even lighter in the case of carbon) weights,energy, & broadhead design (many of the old PC style arrows were not exactly light in most cases by the time you glue adapters, older heavier vanes, and a 100-125 grain head on them). And I also agree with BPS regarding shaft flex. While I have no scientific proof, it is only reasonable to assume that carbon will act the same way on game it hits as it does in inanimate targets. Aluminum bends around like a noodle upon impact..while the softer nature of hide, flesh and ribs may not make for as much shaft oscillation as a foam target, It makes no logical sense that the phenomenon is completely suppressed/negated going from one target medium to the next.

Bow tune is another key factor as I'm sure we all know, and a whole 'nother can o' worms.

Regardless...I suspect this topic, like Singles Vs. Duals vs. Hybrids, Mechs vs. Chisel, vs. Cut to the tip, Open Camo vs. Blend camo. and other similar topics are really only topics of argument started years ago to get us from one season to the next on the message boards and are hardly relevant whatsoever!