I have an GK MB500 and 212 cab (funnily enough, you can view them in the classifieds... ) and although I don't play punk, I've never struggled for volume playing just with back line. I played rock - QOTSA etc.
With that cab the MB500 is pushing out 350w at 8ohms, and I've never needed to put it up above about half-way, so I dread to think what would happen if I put another cab in the mix and got the full 500w...