I guess when I read “punk gigs” I do not immediately assume there is gonna be enough PA even for the vocals or anybody with a clue running it. Maybe y’all have a different definition?
Anyhoo, it’s kind of tough to say how loud a thing will be just by wattage and speaker size. Watts mean different things to different companies and different speakers have different sensitivities and…
If you’re wondering if having two speakers instead of one will make it louder we still can’t answer very well.
If the two speakers are wired in such a way that they have the same impedance as the first, then they will each get half the power of the single, but it’s the same altogether and if they also have the same sensitivity, we’d expect the same SPL output.
If the total impedance is lower than the single, they get more power, and given the same sensitivity, it will be a bit louder. Higher total impedance would actually be quieter.
But even if we knew exactly all the specs for all the speakers it’s still kind of tough to really translate the numbers to how it will actually sound and feel IRL without being there.
I tend to think that if everybody in the band can hear you well in rehearsal, it’s probably at least close to loud enough. IMNSHO though, for a punk band, if anybody can hear the drums, the guitars are probably not loud enough.