UtahRob
If the animal is at the right distance and the shot is placed where you want it - that 300 XTP will do just fine. The confidence of the shooter to make the shot is the biggest thing and you certainly sound comfortable with your set-up
I myself, for elk shoot a 300 grain also, but I have been shooting a .458 (45-70) Nosler Partition in an MMP .458 Orange sabot. The price of lead is going up steeplyso the price of Noslers is climbing also - I am now experimenting with a .452 Speer 300 grain Gold Dot. It is a bonded bullet that should stay together in an elk.
Good luck on the hunt - just remember when hunting elk - the work really begins right after you pull the trigger.