Underpowering is nonsense. If it wasn't, then all amps would on have on/off and no volume knob. Get an amp that sounds good, get a cab that sounds good, and don't worry about numbers, especially power handling numbers. The vast majority of power handling numbers on cabs are done by rating what it takes to melt the voice coil, while real world performance will be a good bit lower. Then use common sense and your ears to keep them from blowing.
