Momentum is the key physical factor that you have overlooked. Here is a calculated momentum for your weights that you have listed. For this im going to use all of the same arrow characteristics (fletching length/height/OD of arrow shaft/shaft length)so the momentum calculatation will be of equal testing.
here is the momentum (lb-sec.) that your 398gr. arrow at 265fps provided. (0.4676332357896604)
428gr. 255fps (0.4839052939611599)
500gr. 231fps(0.5121042830540038)
notice that the momentum continues to rise as you add weight but lose speed...
KE is NOT what makes an arrow pass thru. It is the impact that you arrow gives when it FIRST hits an object. KE does NOT mean that you are going to get good pass thrus.
An arrow needs momentum to get a pass thru. not so much KE. My 101st Airborne that i used to have would shoot a 308gr. arrow at 320fps. It would shoot my hunting arrow which was around 415gr. at 285fps. The KE was really close, but would you want to use a 308gr. arrow hunting??? Yes it may hit the deer with X amount of KE, just as the heavier arrow did, but it would stop so much easier that the heavier arrow since it had the weight to continue to push it through the deer.
Like TFOX said, im not here to preach heavy or light, b/c ive killed deer with both, just stating some facts. Shot placement is key
Derek