SVC sub x 2 vs. DVC sub

So here is the interesting (and fun) dilema I am now faced with...

For the near future, I have installed Polk dB650s in the front (FL/FR/RL/RR) of my Suzuki powered by a Blaupunkt GTA4 amplifier.  I found a great deal on another Blau GTA4, so I bought it.  Now, one feeds 55 watts to the front channels and the new one will offer 170 watts by two bridged at 4 ohms.  My question is this:

What is everyone's opinion on whether a single dual-voice-coil sub would be a better choice than two single-voice-coil subs?  I listen to a lot of "technical" music (think Rush, Ben Folds, a little bluegrass, a little classical...) that demands a fast, responsive, articulate sub-bass range.  I don't listen to much rap so I don't need anything that could be described as "boom".  My initial thought is that a two-sub set up will allow for less excursion of the woofer to produce the same volume, thereby retaining greater linearity, faster response and generally cleaner sound.  Is this correct? 

I'm not concerned with how "low" I can go, as most of the subs I have been considering have similar F3 (no matter the size or configuration).  I simply want the best reproduction of fast, clean bass I can get.  Whadda y'all think?

A good sub will have plenty of linearity in its travel for your normal listening.  The voice coil travel in normal use will not affect the "speed" of the sub;  your properly designed / constructed sealed box is the key to that. 

Using two subs is normally where you want more loudness (or bling!), not where you want better sound quality.  Most SQ systems employ one sub.  By using two subs you introduce other factors that can affect the sound quality of the subwoofer system.  Two cones, separated by distance, different paths of sound waves, plenty of things that would sum to a greater possiblility of SQ deficiencies than just the normal voice coil travel of a single sub.

Use either a DVC or SVC, depending on what impedance you want to end up with and what amplifier you want to power it with.  I would suggest a SVC 4 ohm sub powered by a mono amp, so that it ( the amp) performs as cleanly as it is rated.  A DVC 2 ohm sub wired in series would do the same thing.