Your .308 load is indeed a good one for deer, but the Ballistic Tip is a fast-expanding bullet. It will kill elk handily with broadside shots that avoid the shoulder, but won't reliably penetrate elk shoulder bones. For elk I'd switch to the 165-grain Nosler Partition; you won't even have to change your powder charge, and the load should shoot close to the same point of impact as your deer load. The .300 WSM will shoot a little flatter, but out to 300 yards (about as far as most of us should sho0t at elk, or any other game) you won't see much difference. It will also kick about twice as hard. If you're going to do a lot of elk hunting, you might consider one, but if you're just going on an occasional hunt, you're much better off with a rifle you know and love.