The 300 WSM will do very well on moose [assuming good shot placement and appropriate bullet selection] and it is more than necessary for deer.
Like Wildcat said, if this is your first gun, then I'd recommend against a magnum.
The X-bolt is a great gun. I own 2. They are light and accurate. Because they're light, they will deliver more felt recoil than a similar, but heavier gun. Mine are both in magnums [7mm WSM and 300 WSM]. They kick, but since I've been shooting my whole life, I'm okay with it. If you are experienced, and also don't mind recoil, then I'd say this a great combination of rifle and cartridge.
If you're new to shooting, then you should get something that helps you focus on fundamentals, and that will be more easily accomplished with a lighter-kicking setup.