Aluminums have their good points, but it is no coincidence that about 95% of the archers (at least in this area) use carbons - or aluminum/carbons. I think the small diameter of the carbons - particularly the Easton Axis and other super slim shafts - will increase the probability of a pass through. Carbons are generally rated on a deflection scale - so a .500 series arrow is flexing 1/2" when a 1.94 lb. weight is hung from the middle; and a 340 series arrow is flexing .34" in the same test. Lots of charts to help you find the right shaft. And, as was stated earlier, with carbons you either have a good straight arrow or it's broken. Not this deal where you wind up with a bunch of not-quite-straight aluminum shafts that are not quite bad enough to throw away.

Lighter arrows are going to shoot a little flatter. Won't notice much difference until you get past 40 yards, though. At 60 yards, an arrow going 20 fps faster will drop about 6" less.