1. The WSM under performs the WM across the spectrum of bullet weights.
2. The WSM has feed and function issues that WM does not.
3. Most WSM rifles are NOT built on a short action. They are built on a standard action just like the WM.
4. Even if the rifle is built on a short action. Does anybody here actually believe that the rifle is going to lose enough weight or gain enough bolt cycle speed to make a noticeable difference? Based on a .25", 1/4" difference in bolt length? I'd be willing to bet that the shot clock and the scale will reveal the ugly truth and that the WSM does not gain you ANY advantage.
5. My experience with WSM is that it does not feed as slick as the WM and any perceived extra speed in feed due to length is lost due to the stubby case design.