I like the Weatherby cartridge, in a 700, simply due to the longer neck which allows more latitude in seating without seating below the neck/shoulder juncture.
There are a couple of things to keep in mind. First, if chambering for either cartridge, the length of the throat can be whatever you want it to be; assuming you have the capability. With this being the case, magazine length might be more important than anything else. Modern, high BC bullets are long but their bearing surface is not always all that long. So it is that the shorter 300 Win Mag might work better simply because the neck is further from the front of the magazine.
Another way to look at it is this: the location of the bullet in the magazine is a given; lets say 1/16" from the front of the box. This is as long as you can seat it. This means, if you want to be able to touch the lands, the distance from the bolt face to the lands is predetermined. The point is; you can cut either chamber to provide this length. The 300 Win Mag will be throated long and the 300 Weatherby will be throated short.
Now, if you do this, the Weatherby, because of its longer neck, will allow you to seat shorter bullets out further to touch, or, at least approach, the lands. This is important only if you want to shoot a shorter bullet. Not everyone is concerned only about BC.
As far as achievable velocity is concerned, the Weatherby will have a slight edge simply because it is a little bigger. But it won't amount to a lot.
I have to confess that I dislike the 300 Win Mag because I think the design of the cartridge is just dumb and I don't like the short neck. Because he also has a short neck. 'Stick isn't bothered by this and, in fact, embraces it as a positive attribute (this takes some mental gymnastics). GD
Short is an endearing word for him. If you lived your entire life and had to stare up at someones crotch all day you would suffer from the same issues he has.
