I've been doing some research and can't seem to find some solid evidence about this one. I'm not comparing different calibers here, but merely the rounds within any set caliber. Using the muzzle energy calculator up top it seems that in general, energy transfer from slow and heavy rounds are fairly similar to those of fast and light. In some cases, it seems like the quicker rounds might have the advantage. Many people online say that slower rounds are better for human sized targets, but what is this based on? The only thing I can think of is potentially less fragmentation on slower rounds, but in some cases a certain amount is actually good. I came to this dilemma while trying to choose a self defense round for my XCR. I currently have Speer LE Gold Dot 55gr JSP and Winchester 64gr JSP being considered. Now these aren't the best to pose the question to since the winchester in this case is much more destructive, but all things being equal would you choose a 64gr round at 3000fps or a 55gr round at 3200fps? Please don't get into over penetration nonsense here. Consider it not being a factor, we're outdoors.