Dufus,
How far away is "No man's land?"
No rifle cartridge has ability to knock any big game animal off of its feet.
Biology is controlling. Either destroy a big game animal's CNS (brain) or reduce its blood pressure to zero thus depriving its brain of oxygenated blood.
Here's a biological fact: a .30-30 Win will kill elk just as dead as a .300 RUM assuming bullets from either destroy identical parts, and in this case I'm referring to its heart and/or lungs.
Nothing living remains in that conditions sans oxygenated blood to its brain.
I'm good with any cartridge any hunter wants to use. After all, he's doing the hunting, not me. Therefore, he has to use what's right for him. Where he'll cause my brain's synapses to misfire is when he attempts to tell me that his .300 RUM will kill deader than another hunter's .308 Win. It won't.
Then we come to the practical side of big game hunting. At Rocky Mountain altitude, holding steady is not realistic. I have a self-imposed limit of 400 yards. However, before I would take a 400 yard shot at any big game animal high in the Rockies, conditions would have to be perfect. I'd have to have a solid rest. I'd have to have an uninterrupted shot (nothing in the path of my bullet). There would have to be no wind. The animal would have to be standing still as a rock. There would have to be no other animals in front or in back of it. There would have to be no way that I could close the distance: I'd rather shoot at a hundred yards than 400 yards. And I'd have to be certain that my bullet is going to kill as opposed to wound an animal. We know this as ethical hunting.
Big game sniping is not a sport nor is it hunting.
More practical stuff. Big cartridges almost always imply big, heavy guns. From experience, I can tell you that where the air becomes thin as a dime, you'll feel every ounce you're carrying. Worse, bench shooting, where confidence is born, is harsh when shooting big guns. Big guns = big flinch. Flinching does bad things to confidence.
I once watched a studly, well put-up dude trying to sight in his brand new .300 WM. It wasn't working for him, not even close as evidenced by his solid 6" group at a hundred yards and his flinching. He couldn't finish a box of cartridges because his shoulder was too sore. He said he was going to use his uncle's .25-'06, which is what he should have bought.
A couple elk seasons ago, one of the guides in our camp told me that he'd much rather have a hunter show up with a .270 Win he can shoot than a .300 mag he can't. His hunter had a .300 WSM that he couldn't shoot. He missed a huge bull twice: once in the am and once in the pm. Had he put a .270 Win through that bull's heart, he'd would have been done hunting just after dawn of opening day.
Were I accorded a hunting do-over, I'd buy a good-quality .280 Rem and never look back, and it'd be the only big game rifle I'd need for all North American big game hunting. If we were to factor out the .280 Rem's ability to shoot 175 grain bullets that have legendary penetration ability, the .270 Win would be just as good.
There is reason that the .270 Win, .308 Win, '06, and 7MM Rem Mag consistently rank within the top ten of yearly purchases of big game rifles.