This will likely be interesting...
As with self-defense against humans, caliber is usually irrelevant
Grizzly have been downed with a single shot of 22 rimfire, 9mm, 30 Carbine, and a host of other supposedly "inferior" cartridges
Look at the long LONG history of successful black powder hunting and self defense use against Grizzly
But what about the numbers?
You
need xxxFPS, you
need xxxFT/LBS
Archery anyone?
Bottom line...
As with human self-defense...
Practice
Placement
Penetration
Trumps everything else
(I know this isn't quite the path you were after OP, but I like to preach this stuff every chance I get
)