Can't help you with the Montana.
I have a Kimber 308 I'm very pleased with, but I wouldn't want one in 300 WM. They are good quality rifles, but the premium you are paying is for a rifle 2-3 lbs lighter than the competition. Not a good idea with a 300 WM. My 6 lb 308 has almost exactly the same recoil as a 7.5 lb 30-06. Certainly tolerable and I feel giving up 100 fps to save 1.5 lbs with no difference in recoil is a fair trade-off.
If you do decide on Kimber I'd suggest staying with 30-06 or 300 WSM instead. Kimber makes 4 action sizes. The short action 84, long action 8400 (which the 300 WM comes in), the 84L sized for 30-06 length rounds and the short action 8400 WSM designed just for the WSM rounds. If it has to be 300 WM I'd go with the Montana, or some other route.
The 8400 action size is just all wrong to me. The feel, balance, etc just isn't there. It is hard to describe until you hold all of them side by side. The others are just right. The 300 WSM will be about 50 fps slower than the 300 WM. But it uses 12-15 gr less powder resulting in noticeably less recoil which is a plus in a lightweight rifle. No game animal will ever notice the difference, you'll never notice any difference in trajectory, but your shoulder will thank you.