So the consensus seems to be that 2 AC15s won't have as much headroom as one AC30. I might eventually try to find an AC30 some day, because I'm still infatuated by the sound of my AC15. I've had it for over five years, and have done many gigs with it (even a few tiny one's where I actually sang through as well!) and it has never let me down. Even a SF Vibrolux or a 5e3 copy which I bought more recently haven't made the Vox redundant.