of the above, MCgunner is the only one who actually probably knows what he's talking about.
The .257WM is an excellent cartridge. With the 120gr Nosler Partition, it'd do what you want it too.
Is it the best possible choice? Perhaps not. But a rifle purchase is as much emotional as practical.
Practical ? Get a Savage M110 or Remington700 synthetic, mount a GOOD 4x scope, sight in with 180gr Federal/Nosler Partitions. Go hunting.
The .257WM will not be "optimum" for the Moose, but for Elk or lighter will do nicely. It will do the job on moose though. I know some who have killed many Moose with a .243, and others swear by a .30/30 with 170gr Rem.CorLokts factory loads. Moose though quite large, are not particularily hard to kill. Pound for pound, the whitetail deer and particularily pigs are harder to kill. For Black bear, the .257WM will do well. Largest blackbear killed in Georgia ran over 600lbs. Was killed with a single shot from a .243.
I too have a .300RUM. I'd not "recommend" it to anyone for any reasonable use. Not a bad rifle, but too much of everything !!!!! (But I do "like" it!!)
If you don't get the .257WM, get a .30/06. It WILL do most everything acceptably well. But, so will the .257WM. Recoil is about the same, trajectory is much in favor for the .257WM.
My .300RUM will probably at some future date sport a .257WM barrel. But, my .257Roberts will do nicely too.
It "HAS" taken an elk. Did better than my .338/06, too.