The 338 Edge is quit easy to load for.
The 338 RUM lacks NOTHING comparing the two. The extra case capacity is of little use because you don't need to push either load for accuracy or distance.
The gunsmith who built my 338 Edge built a 338 RUM just to prove that point. You would never notice the difference behind the trigger.
Take your pick. If built by a good smith, you'll be in hog heaven