As Ajo said shot placement will make any bullet work.. Is the reason you want to use a 150gr bullet because your gun shoots the best groups with it or because you like that weight the best? I would step up to the 180gr. Not sure if you have tried a heavier grain bullet in your gun or not.
I'm sure a well placed bullet will do fine, but like others have said here, I go with a 180gr in .30 caliber for Elk as well, leaving the lighter bullets for deer. I happen to use the Nosler Partitions, but get a good penetrating bullet like mentioned above as well.
If you pick up a reloading manual that has a balistic table in it you will find that the magnum calibers were designed to shoot the heaver bullets for better performance of game. The light bullets will work but then why did you buy a magnum rifle speed isn't everything.
Have you thought about a trip out west for big game? Have you dreamed about what it might be like to ride horseback through the beautiful Rocky Mountains, while looking for deer or elk? Have you dreamed maybe of traveling to Canada for a moose, elk, bear or deer hunt? Have you wondered what it might be like to see the wild Alaskan bush?
Well, I have a little advice for those who have wondered those, or similar thoughts. JUST DO IT!! If you think you might enjoy it, my bet is that you...