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.
Hunting can be slow and frustrating if Mother Nature throws a warm hunting season at you. But things can take a drastic turn for the better with the onset of a cold snap. Whether you get snow or just a good, prolonged cold front, the hunting can improve on a dime. But cold whether can also make certain parts of the hunt more tedious. Here are some things to keep in mind when your prayers for cold weather finally pay off.
You can see a your quarry's breath when it is cold outside...