Mike - I'm behind the times, haven't visited this forum in a while. Congrats on a great bear, taken with a great rifle.
I got a pretty good Washington bear, chocolate, in 2010. Not nearly as big as yours though! Used a .375 H&H Ruger Number One, and a single 260 gr Nosler Accubond at a tad over 300 yards. Instant thump down. Are the .375's necessary? Of course not! But they're a lot of fun to use for sure.
Again, congrats, and thanks for posting those great photos. I dearly love bear hunting, my son and I have been out a couple of times already this season, no luck so far.
Regards, Guy