Ripper, Welcome. I've been shooting a .338 x .378 that I started building 4 years ago. I keep changing things; stock, scopes, mounts/rings, muzzle brakes
, loads, etc. I recently decided to shoot only 300gr Smkhp's and am concentrating on loads for that bullet.
The cartridge has what I believe is a well deserved reputation for being difficult and expensive to dial in. So far my best load with the 300gr is 3/4 moa (repeatable) at 2760 fps out of a 27 1/4" barrel. I am confident that it can shoot 1/2 moa when I find the right combination. As it is, this load can deliver nearly 1000 ft/lbs of energy at 1 land mile, and I think that I can load it up to 2850 fps without a problem.
The .338 RUM doesn't have the reputation for being finicky, and neither does the Edge. Also, brass is about half the cost of the Wby.
I'd have to say that either cartridge makes more sense than the Wby, but I rarely let good sense influence me.
I just really enjoy this rifle, and have no wish to switch to anything else.
This is a good choice to have to make. If you build a custom rifle
, either cartridge should be great. Also, the Rums can be built on a Rem action. I wouldn't put the .338 x .378 in a Remington action. A MK V or a big custom action would be my choice.