In college I had a botany professor who did research in the Artic in the summers. A couple of girls in my class signed on as summer research assistants. They were issued .357 Magnum hand guns and given shooting lessons. The professor's lab had a sign that read "Stop. There is a polar bear on the other side of this door." These signs adorned all the quonset hut doors in the Artic. They take polar bears seriously up there.
Before last year the Park had not had a grizzly caused human fatality in more than 25 years. The Soda Butte attack in '10 was really amazing. I still suspect someone antagonized that sow, but that's of course just specualtion.
I think every mammal capable of snuffing out your flame in seconds deserves respect. In terms of the discussion in my understanding Black Bears are responsible for more human fatalities because their are more of them, especially in close proximitiy to more dense human population. As has been implied already I too think Grizzlies are more likely to stand their ground or charge, or act predatorialy.
I'm not sure a rifle is a good choice for defense against a Grizzly. If I carried a gun it would be a shorter shotgun, or large handgun with shot shells. I do my best to not suprise predators out there, I don't wear one of those annoying bells, but I do have spray and an airhorn holstered at hand. When sight distance is limited I make a bit of noise. Enjoy your hike, just take simple precautions.