I doubt there's any ballistic difference between the .300 Win Mag and Win Short Mag version. Both burn the same amount of powder for a given bullet weight and produce the same muzzle velocities. Differences between individual rifles may exist, but that happens with all cartridges. And a 1 grain difference in charge weight for exact peak pressure levels may be reality, that's meaningless for all practical purposes.
Accuracy with either will be the same from barrels with the same bore, groove and twist numbers. The WSM version is easier to reload for as it doesn't have the belt that's a nuisance to deal with, but can be managed.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master