A subwoofer properly setup so it is augmenting the main speakers and filling in the few holes in the room shouldn't need to sound "fast".
Why? Because at 30Hz or 40Hz there's really no such thing as fast. The whack of a drum doesn't sound like a thud because that initial whack comes not from the subwoofer but from the bottom of the woofers in the main system. The sub handles what follows in the low frequencies.
Now, there are always exceptions. I remember when we were designing subs for Genesis and measured differences in transient response between different amplifying schemes. That said, those differences never manifested themselves in the listening room as faster or slower.
What's important in a subwoofer, once properly set up, is the level of distortion, the freedom to move in and out (excursion) without any restrictions, and amplifier power.
Fast? That's a function of your main speakers.
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