Pick your poison. I have two 7mags and a two 30cal mags, the 160Xbullet in a 7mag will kill ANYTHING on this continent with ease. If you WERE going to use it for griz then I'd step up to a 175Xbullet but realistically if I'm goin for griz then I'm buying a 375H&H, you'll spend THOUSANDS (usally TENS of thousands at that) to hunt them today so an extra rifle isn't going to break the bank. Comparing the .284 to the .308 is splitting hairs. I likewise have a .280 and two 30/06s, one will do anything the other will do.
I LOVE rifles and have a weakness for them, the dozen plus I have today will probably grow into multiple dozens by the time they throw dirt in my face. That being said, if I could only have 2 rifles I'd probably own a 7mag and a 375H&H. But to go even simpler, if I could only have one for doing it all... probably would have to get a .338Mag!!!
Btw, if she's buying you guns now and aint even legally yours yet, you probably should snatch her up and make it legal. Gooduns like that are hard to find!!!

HL