Looked up the ballistics table on the Winchester website...

300 Win. Mag.
180 Grain
3.340 inches (cartridge length)
2,960 fps
-11.9 inches at 300 yards
3503 ft. lbs

300 WSM
180 Grain
2.860 inches (cartridge length)
2,970 fps
-11.7 inches at 300 yards
3,526 ft. lbs.

If I read that right the WSM is faster, flatter, and harder hitting???

f.y.i.
Shane