When considering penetration on big game animals the size of elk, etc.. I think you need to look at more than just KE. Momentum should also be considered and I think that what the above suggestions are somewhat referencing is that by going to a heavier arrow you are increasing your momentum while keeping your KE at about the same level.

My typical setups have been normally generating between 70 and 75 ft. lbs of KE with a 420-440 grain arrow. I have not run the numbers through Jackson's KE calculator for me new bows....yet. I would have no hesitation about using my particular whitetail setup for just about any other big game animal in NA provided I am using the correct broadhead and my shot placement is there.