Yep what that guy is saying about efficiency in the video makes sense. You can't get more bass out of essentially the same size package without losing some efficiency so the I would tend to lean towards IIIs with lower power amps.
I heard IVs with a beefy Anthem solid state amp and that was a very good combo.
If you want flat extended bass off a few watts you need big speakers. No way around that. It's the laws of Physics.
