I've been using the 8 ohm versions for 6 months now in my bass rig. I love them. They aren't quite as efficient as listed. They have no high end and limited mids. I use them in three way cabinets with Eminence 6.5" mids crossed at 800Hz.
The 8 ohm versions state 30Hz as the low end and put out sub-like lows, but tight and punchy. I have them in modified EV TL806 cabinets.
I would guess the efficiency to be closer to 92-94dB, compared to known 15" cabinets I have. I push the cabinets with a PF500 and even at outdoor gigs I have plenty. I absolutely love the cabinets I built.