LAST EDITED ON Mar-25-12 AT 10:43AM (MST)[p]You can't go wrong with a .338 win mag or .375 H&H, as long as you can shoot them well. Heck, for a guided hunter, a .300 win mag or one of the other .300 mags would work fine too.
Personally, I shoot a .338 for nearly everything, including a nice bear I took on Kodiak, using a 250 grain nosler partition.
I do not think I'd shoot Accubonds for big grizzlies, as you suggested your considering. I'd stick with something like a nosler partition, swift A-frame, trophy bonded bearclaw or barnes ttsx. The accubond is a great bullet, but I don't think it'd be a best choice for big bears. Unless you're shooting at a wounded bear, you won't be shooting over real long distances, so I'd go fairly heavy for caliber, you can never go wrong with that when hunting dangerous game.