I shoot a 300 win mag and my friend has a 300 ultra mag that I've personally shoot a bunch at the range. While the Ultra mag has more velocity and more energy for practical hunting situations for most guys it's not worth the extra recoil and price tag on the ammo. But if your going to set it up tactically for 400-800 yards across canyon shots it's has it's place in the hunting world. But that's a lot of range time and information to have to learn to shoot those shots. I know of three bull elk that were found days later after shooting over 600 yards across canyon just last year. These men didn't even know they had hit the elk until the magpies and crows showed up where the elk finally died. Very sad very true.
My opinion is if you can't get it done at 500yards and under with a 270win, 30-06, 300win you probably don't have any business with a 300RUM at 500-800 yards. The cartridge isn't going to help you shoot better. Not trying to be too opinionated but I see this year after year with new clients bringing super mags and can't shoot them at all.
I'd like to share just one instance to prove my point that they are not made for everyone to use.
Had a guy show up with a Lazeroni .308 warbird which is even faster than the 300RUM. He could shoot a reasonable 1 1/2" group at a 100yards. So off we go elk hunting. We spot a bull elk on the mountain at 428 yards. His gun is set up all tactical and I just assumed he was going to set up and take that shot. I asked is something the matter when he didn't and he said I can't shoot that far we have to get closer. So off we go stalking up and around the bull because of terrain. Hour later and 5 shots we have a bull go down at 80yards from us. I asked him why he even brought that gun in the first place he said everyone at home told him it was what he needed to buy for elk. I have many stories just like this one and they could go on and on and on. I think you get my point.
I like the 300RUM I like shooting it. And I would like one set up for shooting across canyon at long distances. But it's not for everyone and for sure not for a typical hunting situation. I would considerate over gunned in a lot of peoples hands.