I mean, what is better for you? I went through this exact same dilemma a little while back and settled on the WSM because of the availability of the Lapua brass and the fact that I see more factory ammo available over the SAUM. The factory ammo is only a consideration for me because I like to have that option available if something goes wrong with handloads, forget them for a hunting trip, having a few boxes on hand, etc. - which is what ruled out the 300SS for me, anyway.
Just looking into the three of them, the numbers are all close enough I think you'd be hard pressed to find a meaningful difference in performance. What are we looking at, less than 100 fps difference between the WSM and the SAUM? The 300SS claiming 3000fps with a 200gr projectile is marginally faster than the WSM, allegedly. It's dealer's choice, at this point.
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