The 300 grain arrow at 300 fps would have 60 ft/lbs of KE, just like in your example. I'm going to increase it by 17%, which would require shooting the same arrow 325 fps. Regardless of what draw weight is required, will it deflect equally when compared to a 600 grain arrow shot at 230 fps when entering flesh, hide and bone. I believe the lighter arrow in this example will deflect more. It will have the same KE as the heavier arrow, but it's momentum will be less. It's energy will be diverted off it's path more easily.
Straightarrow, I understand what you are getting at, and you are not incorrect from a pure momentum/ke perspective. I have said on several occasions that energy as a result of high mass rather than speed is better for maintaing path and "breaking" through bone. But the choice you present is IMO not properly stated. You are implying that the archer is makeing a simple choice between KE and momentum but that is not the case at all. It's not like my case which changes only the weight of the arrow. The real decision you present is do I go after more penetration potential by increasing the stored energy in my bow or do I go after it by putting on a heavier arrow. This isn't a momentum/ke decision. If you can store more energy then you should do that first. The decision to pull more weight should have nothing to do with anything other than your physical ability to control it accurately. The more potential energy you have, the better off you are. You can always put on a heavier arrow too if you want even more penetrating potential.