Re: 300 WSM-300 Win Mag: Accuracy, Load tuning, Case life.
They are the same in a long action.
In a short action the Winchester has a significant advantage with the 230 Vlds.
The 300Win is about the most agreeable chamber you could ever want to shoot. H-1000, H-4831, RL-22, IMR 4350, IMR 4831 are all fully capable of shooting bugholes. With H1000, H-4831, and RL-22 the 300Win shoots best wide open and if you want "magnum velocity" these are the powders to start with.
Both are great rounds, but I prefer the standard 300Win.