Seems they all use LARGE calibers for backup.Outfitters don't typically seem to be up to speed on terminal ballistics and why. That said, the outfitter I used for dall/griz had no concerns with me bringing a 6.5. Overkill compared to the sharp sticks he kills both with. If I had to pack today to go back I'd be bringing my 6 creed.
Assuming the shooter can do a good job with one, why wouldn't he use one too?