High Sensitvity = good transient response ?

To the excellent responses above, I would just like to add this readdressing of the thread-head's main question: Yes, it is perfectly possible to achieve good transient response from a speaker design of average sensitivity. But I would also like to point out that the real-world transient response of a given speaker is going to depend a lot on the amplifier driving it, if your definition of "good" transient response means following the impulse accurately without excessive overshoot, undershoot, or overhang - and in the case of a lower-sensitivity speaker, this may require more from an amplifier. Some other things that enable a speaker to accurately track transient impulses include the drivers' ablility to resist compression through efficient heat dissipation, a non-resonant-in-its-operating-range (or well-damped) and rigid-yet-low-mass driver surface, and a wide linear (undistorted) travel range; a rigid and non-resonant mounting and cabinet (if there is a cabinet), as well as rigid coupling of the speaker to a non-resonant floor (or stand and floor); and a high-quality crossover construction that does not introduce its own delays, compressions, or resonances.

Cdc, the physics of speaker and driver design basically dictate that if you're attempting to reproduce (almost) the whole frequency range with just one driven element, you're going to have to give something up. It could be efficiency, dynamic range, extended bandwidth, optimized dispersion, etc., or a combination of some of the above. The payoff is supposed to be in the quality of "seamlessness" or "coherence" that comes from not dividing up the amp signal, not using different driver types or materials, and not intoducing lobing or phase anomolies, as well as possibly making an easier electrical load without a crossover for a low-powered amp to drive. In your above example, I'm assuming that the amps were also different, which would have something to do with what you heard (as would the rooms and setups), but yes, it's quite possible that a conventional multi-way speaker could exhibit superior bass dynamics. (BTW, what are the tolerances and conditions given [-3dB down or -6dB down? Anechoic, nearfield or in-room?] for the bass frequency response ratings you mention? If they're not the same, then you can't compare the ratings directly.)