Your looking at about 200 fps more than out of your rem. mag

lots of gunsmiths will rechamber your barrel to the shooting times westerner.

The STW is about equal with the 7mm Rem ultra mag. You can use 8mm remington brass to make 7 stw or buy factory 7mm stw ammo. I would look into the 7 ultra mag if you do not plan on reloading. I don't know what stores are like in your area but here in utah it seems the 7 ultra mag ammo is more available.