Let me rephrase my prior example. If I'm trying to get the least amount of deflection, should I concentrate on getting my 300 grain arrow that flys 300 fps, up to 325 fps (a 17% increase in KE), or should I try to increase to a 600 grain arrow that flys at 230 fps (also a 17% increase in K.E)? I do not believe penetration would be equal, yet the increase in KE would be equal. The arrow with the highest momemtum will penetrate furthest when hitting a mixed media, where deflection is likely.
This is a much different example than before. We are now changing more variables than just the weight of the arrow. If we assume that your 300 ft/sec 300 grain arrow is shot out of a bow with 85 ft/lbs of stored energy, 65# peak, 30" draw, 8" brace, the stored energy would have to be increased to 99.9 ft/lbs to drive the 300 grain arrow 325 ft/sec. That also means a 11.4 pound increase in peak weight. If you are capable of storing nearly 15 more ft/lbs of energy and are able to shoot it accurately then I would say without question this is the way to go. At 75# though you shold increase the weight of the arrow to at least 375 grains. But of course now you are back to pretty close to 300 ft/sec but with more of both ke and momentum. See what I mean?