The short action advantage of the WSM is a pretty much a bogus issue for most hunters unless you are going to be hiking for miles into some remote outback. And even under those circumstances there isn't enough difference in the weight (if any) of 270 wsm and a standard 270 to matter much. The thought of someone being perky and fresh after a mile hike with a 270 wsm yet dragged to his knees near death by a 270 is silly at best. I know it is widely stated that the design of short action bullets are inherently more accurate but again I think the differences are microscopic at best. There are so many factors that affect the accuracy of a particular gun that the odds of this type shell improving yours are minis
Have you ever used a short action anything to make a statement like this and hunted with one? Have you chronographed any loads to make a statement like that?
If I had a choice between a 7mm mag and a 7mm WSM I'd get the 7mm mag. Same deal with the 300 mag and 300 WSM. The difference in bullet drop and ft lbs of energy are not enough to make any appreciable difference in any hunting situation in my neck of the woods. Availabilty of bullets, price and the comfort of knowing I had a gun chambered for a cartridge that had already survived the test of time would be my reasoning.
Have you even shot both of them to compare and looked at current load data for either the 7 Rem mag vs7 WSM 300 wsmvs 300 win mag?