That was in reference to hard-cast lead bullets as a limitation so I was not very clear. Sorry about that. Yes, with Punch bullets and mono-metal bullets, they should always benefit from more velocity. It also follows, a faster RPM to effectively spin/drill that bullet deeper or through solid bone would be the result.
In lighter framed six-guns and five-guns the velocities are limited so the velocity limitations would remain. The resultant recoil should also impose a comfort limit too. If a heavy hard-cast bullet can penetrate completely through a trophy Cape Buffalo broadside, and then continue on to penetrate and kill a female Cape Buffalo unseen by the hunter on the other side, I would assume that would be an extreme performance and penetration example. Brian Pearce was the hunter I believe. He was using a 45/70 lever-action rifle with a heavy hard-cast bullet.
So a moderate velocity, compared to high velocity rifles, can exhibit powerful penetration. And the heavier projectile provides the momentum for the extreme penetration.
I just want to be clear though. An A-frame has the characteristics of expansion as well as retained weight for deeper penetration. Greater velocity can help with that bullet also. I am of the opinion that revolvers are best for BIG GAME with BIG BULLETS of over 40 caliber and up. The velocity is not going to reach over 2000 fps with HEAVY bullets, so the random 1800 fps comment was from my memory of a in-depth bullet-test spectacle made some years back.
Just my opinion so add it to the discussion.