I wouldn't hesitate to use a 300 gr XTP on a 300+ lb deer or even an elk for that matter.
Muley I believe that most in here are deer oriented. You and a few others I can understand your reasoning for a bullet that will perform well on elk. And IMO the XTP would stand up to the task. And as I recall you like to get close like me and prefer the .54 PRB and traditional gear.