There's plenty of combinations of bullet and velocity that can yield nearly identical energy results on paper.
Would the target know the difference, though?
Bullet design no doubt has a considerable influence, too.
In this example, with both versions differing only by weight, length and associated velocity, different amounts of penetration could be expected.
How much it matters to a Grizzly would probably depend on the size of the bear.
And the answer to the question would be the common one of "it all depends."
(Would the speed of the charging bear have an effect on the bullet velocity
)
While on a fishing trip in eastern Canada, a friend and I were chased by a very large brown bear.
(Did you know they can run about as fast as a horse?)
Some critters just don't like unexpected company.
Unfortunately Canadian laws didn't allow us to bring our .44 Magnums, so we never found out what would stop a big and angry bear.
Having our car parked close by probably was a better solution anyway.