There are many assetions on here as Phil says. The one I woud like to hammer is that any 4x10" can out perform any 1x12". It depends on the drivers, the cabinet design and the personal preference of the player.
I should also point out that Dave Greenboy originally designed his cabs to be bi-amped*, as he felt that this was a better option than using large power crossovers. In that case using multiple drivers is no compromise. In fact the acoustic power (max SPL) output is greater, less heat is generated, less power is lost in both crossovers and drivers.
*Bi amping uses small signal, solid state crossovers.