I don't see a problem using them on bunnies or other small fodder. Their spherical shape makes them quite strong in tinking of impacts on bone or tissue. As to super high velocity, I can't comment.
in the .69, when shooting snowshoes hares with WW balls I used a mere 30gr. 3F. My buddy then using a .735" WW ball in his .75, used a mere .40 gr. 3F. These loads worked well to 50 yards, and the sound of their bones breaking was later that the funny sound of the gun - kinda like peeoughhh/crunch,crackle/crunch - only faster - HA!