Hello, there is not that much diffrence between the two. If you compare the long range trajectory the WSM is a little better. The short fat column burns powder faster simular to the Benchrest and PPC wildcats. Becareful when buying a rifle chambered in short magnums make sure the action is actually shorter. The Brownings are chambered this way. Some of the other rifles manufactures chamber these newer short magnums but do not have any diffrence in bolt throw. You can compare balistics on Winchesters and Remingtons web sites. Compare apples for apples like 180 grain Power point VS pointed soft point(basically the same bullet diffrent brand).

Personaly I would buy a 300 Remington Ultra magnum Not the SAUM(short action ultra mag). The 300 Remington Ultra Mag is more powerful than a 300 Weatherbee mag. Since I reload there is not that much diffrence in the price of the reloads. I own a Ruger Model 77MKI in 300 win mag and love it. I wouldnt buy another 30 cal to replace it But If I bought a new gun today I would buy a newer caliber.(better resale if you ever need to sell)

Remember though if you dont reload then you are going to pay more for this newer caliber ammo. Winchester and Remington want to sell ammo Period. Its residual income for them, you need ammo to shoot. Winchester cornered the market on these short mag rounds. Remington came out with the Ultra Mag first(1998??) and had to hurry up and try to sell SAUM's to catch up with Winchester. Check out the prices on ammo you will see that the short actions and ultra mags cost more.

Just my 2 cents
good luck
Jay