I appreciate the fact that at least you are talking about stepping up in caliber enough to make it worth while. The 30-06 ain't bad. I find the 338WinMag to be a bona fide elk rifle (in the varmit, deer, crossover, elk rifle, elk hammer, .... continuum). The 338RUM is a winnie on steroids, even stronger.

Per the parameters of your question regarding the 338RUM you have found at a good price.... I'd have to say yes --- good choice, conditioned on the following....

The question in my mind is, "Will you spend the time and money to get some top notch instruction from a certified NRA insturctor, who ALSO likes big bores, on how to handle it WELL?" When you move up to that level of play there are a whole different set of factors in the mix that demand proper technique and equipment fit. I'd hate to see you buy it, get "introduced" via the "school of hard knocks" and then sell it in 6 months because, "Mama, it hurts me and I just can't hit with it!" [Even much more so for a 378 Weatherby!]

EKM