RE: Whats the best biggame caliber?
IMHO, there is no such thing as a "best" big game caliber or cartridge --- depends on too many variables to name just one.
Also, IMHO, the 300 RUM is not a particularly "big magnum". Nice cartridge, frisky, flat shooting, hard hitting small bore, one I'd consider buying, but is not a "big magnum".
Just my $.02,
EKM