My answer may not be wizbang popular, but if you have a 30-06, you have plenty of rifle for elk. I would recommend a 180 gr. premium bullet or heavier, but I have yet to see the situation with elk where a decent shot with a 30-06 180 gr. partition had to back up and pass on a shot that another rifle cartridge would have solved.
I once had a man work for me that shot two bulls within about 20 seconds with a 25-06. They both expired in short order. I am not condoning his ethics, - just his rifle choice. He was hunting with a buddy (not me) and decided to fill his tag too. His ethics sucked, but his ability as a shooter is not in question.
If a man wants to shoot something bigger and needs to justify it, then power to him, but I never have bought into the idea that today's elk are tougher than yesterday's.