I'm going in June and I have bought, traded and worked on several rifles trying to answer this same question for myself. I ended up settling on the 470 double as my first choice and the 416 Rigby bolt rifle as a back up. I think the 375 is good as long as everything goes good, but in a bad situation I would like to have a little extra shock and awe on impact. I am seriously considering having a set of 500 nitro barrels made for my Kreighoff as well, probably not "necessary" but I really really like the rifle and the 500 would be really fun. The smart play would be to get a set of 30/06 barrels made for it instead of the 500. I really like the gun and plan to use it as much as possible, whitetail, black bear, hogs, so a set of 30/06 or 375 barrels would be much more useful.
Says the man that hunts whitetail with a 500JEFF, haha. I really don't think the extra 500-700 pounds of energy would be that noticeable IMHO. just food for thought.