This is a "long range" site. Many of us shoot quite a ways out there. Many people work all year tuning thier loads to the best of thier ability so they can make that long range shot. Thier loads shoot bigger bullets with higher sectional density & higher b.c. bullets with enough speed to make them more effective at long range. Try to shoot a 200 gr Accubond with a 308 for example (a cartrige you listed) & there just isn't enough there to push it with enough energy to hit hard at long range -in comparison-. Sure it will buck the wind better, but the bullet never gets a fair chance to deliver energy when it starts that slow -in comparison- to that same bullet from a RUM or simmilar cartrige at long range. Great for punching paper, but run jbm ballistics calc. max speed of a 308 vs a 300 RUM using identicle 200, 210, 230 gr high b.c. bullets. You'll see very clearly why.
The advantage to shooting bigger magnums is strictly to take advantage of higher b.c. bullets wich prove extremely effective the farther you shoot. Less wind drift, & more retained energy downrange is important. It's not a who's is bigger contest.
As for the 2-300 Yd deer thing, would you pass on a great buck because you wanted to go back home to get your smaller deer gun? Or would you scare him off so you could shoot farther? Or would you shoot him where he stood, with the rifle you were carying? Now after all that, would you tell your Buddies about your buck, or would you keep it a secret cause you used your L/R rifle at close range? I haven't had to let one walk yet because of being "overgunned", & I'm not ashamed 1 bit.
Now reverse that situation. If you don't have enough retained energy at long range to be effective, why bother if your intent is "long range" on big game. Many of us here don't just deer hunt with our rifles. Heck, some folks live in Griz country. Why not use a bigger cartrige?
The cartriges you mentioned in your post are all great cartriges. Many folks use them to great effect at long range on a veriety of critters. I'm not pushing horsepower over shot placement. But if you live in a place where you can shoot Deer, Elk, Bear, etc as far as you can shoot effectively, its way more effective to have both horsepower, & shot placement if you plan on taking long range shots.
I guess some folks never get a chance to leave the deep woods & see big open places, & big animals.
Now as for the snide remark you made about "want some advise...?" No. Not from you. Remember this is a long range site. People will use thier chosen cartrige, no matter what it may be, for thier chosen style of hunting to the best of thier ability. That doesn't make it wrong or right for you or me personally.
On another note, I've killed plenty of critters with a 270, & 30-06, from Deer, Elk, & Bear, to varmints. They are great cartriges too. I'm not nocking the 308, or other rigs simmilar in class. They are plenty effective at a veriaety of ranges, including long range, on a lot of game. I shoot larger cartriges now a days to suit my personal hunting style, & places I hunt, & animals I am hunting at ranges from 6 feet to as far as I can effectively shoot. Some cartriges fit the bill better for me than other cartriges that fit the bill for you & your personal hunting style.
and the 270 ofcourse. if you gonna kill big big game than ok 300rum is allright. 
