I really like both of your rifles, but would pass on the 300 WM in favor of the WSM in a heartbeat. I've had both and kept the WSM. I get 98-99% of the bullet speed, but with about 90% of the recoil. The WSM is also proving to be more accurate and is more efficient from shorter barrels. In a nutshell you get near 300 WM performance, in a 308 sized package, with hot loaded 30-06 recoil.
The WSM's have only existed since 2000, ammo costs and availability used to be a concern, but no more. Most of the other WSM's have died, but the 300 took off faster than most any chambering in history. It took 25 years and being adopted by Jack O'Connor before the 270 gained any success. Winchester almost dropped the round. After only 12 years it is well ahead of the 270 at the same time.
I can't recall the last time I saw a store that stocked 300 WM ammo and not 300 WSM. They are now within $2 of each other price wise. Both are too expensive for me to not reload for and I find the 300 WSM much easier to load, and much cheaper since it takes far less powder to get almost the same speeds.