I too have contemplated a 300 Win Mag, particularly for big heavy game, like moose of the larger African plains game. I dream of hunting Alaska or British Columbia, and think of how a 300 Win Mag with 200gr Partitions at 2850fps would be better for grizzly or brown bear. This seems to be getting more into a specialized role though as opposed to a general use big game rifle, and for the very few times I would go on these hunts (probably once if I am so blessed), my 7mm Rem Mag could do the job. I think of Les Bowman, who was heavily involved in the development of the 7mm Rem Mag, said his clients, on the whole, shot noticeably better with 7mm mags than with 300s. John Sundra is a huge proponent of the 7mms, and has said they will do nicely for any non dangerous game.
"The 7 mm magnum, I feel is close to perfect as the caliber for all the lesser African game, including, I might say, the leopard and possibly the lion, for all our North American species that live in mountains, and for all the Asiatic types of both high and low terrain that weigh under a ton or generally don't eat people. ..the sum total of experience is to lead me into the statement that for game from seventy-five to a thousand pounds, especially at ranges beyond rock-throwing yardage this category of cartridge is the most useful we have. It hurts you little, hurts the game a great deal." -Warren Page
Of course, Mr. Page was shooting his rifle, Old Betsy#1 in 7mm Mashburn Super Magnum which is similar to the 7mm Rem Mag
If I do get a 300 Win Mag, it would be simply because I want one, not because I need one.
According to Dave Petzal, The present Shooting Editor for Field & Stream, "Page was essentially a one-gun hunter. He used lots of different stuff, but the majority of his big-game trophies were killed with a single rifle-a 7mm Mashburn Super Magnum. Page got this rifle very early in his career-1949 or so. He called it "Old Betsy," and used only one handload for everything, a 175 Nosler semi-spitzer bullet at 3,050 fps. Throughout her career, Old Betsey wore only one scope, a 4x Redfield with a medium crosshairs.
Statements like this remind me that my 7mm Rem Mag is truly capable of everything I need in a big game rifle, and does so with relatively mild recoil. To me, that is, as Larry Potterfield would say, the nearly perfect hunting cartridge.
If I do get a 300 Win Mag, it would only be because I WANT one, not because I need one. There's nothing wrong with appreciating that cartridge's merit , that makes it a nearly perfect hunting round in it's own right.