Once upon a time we had a sow grizzly in camp with cubs (big cubs). Consensus from the group was what seemed potent at the dock, didn't give the same warm fuzzy feeling at that moment. I'm pretty sure all of us would have traded up. I had a .358 AI magnum, 250 grain Nosler Partition at 3000 fps and I would have. The .500 N.E. I mentioned back a bit wouldn't have been over the top.
Reality 1) If I had the money to buy a good quality double, I'd spend it on a brown bear hunt and take the .375 I've got, but I do understand what it's like to have nothing but a sheet of canvas, a couple feet of night air, and the rifle you brought between you and a critter that considers himself to be the apex predator on this range.
Reality 2) Shot for shot if one was able to evaluate all the Brown Bear /Grizzly kills that have occurred (not pull single incidents to prove a point) bigger would prove better.
Pepper spray is better than firearms is the new claim I hear a lot, but thats not how I'd bet my behind (or yours if I was responsible for it).
Here's hoping all of you get a real world chance to test whatever your personal favorite is on the biggest bears out there.