Unless the '06 doesn't fit properly, then I would definitely pass on the 338winmag. Its a pretty big step up in recoil. The 300winmag will be a noticeable step up, but with a good recoil pad, it can be tamed. My wife handles a 300 in an Xbolt. If you do a 300, just shoot a couple rounds at a time at the range, or just until the fun factor starts to wear off. Put it away and go home. You'll find that after a while, you'll get used to the kick, and won't get a flinch. If you get a flinch, you might as well sell the thing. I did this, and went from a 30/30 that I swore was evil, to a 7mm mag, to a 300RUM. So it can be done.

That said, and not to discourage you from buying a magnum, there is nothing wrong with an '06 for elk. It has plenty of power for them within its limits, and every year alot of them fall to the '06. If its your story to the wife to convince her you need more guns, well then, thats our secret,lol.