Choosing a Sub

Hello,

I have two Rockford Fosgate 501s amps and would like to bridge each of them to two 12 inch subs. I have a choice of the Infinity Kappa Perfect 12DVQ Dual 4 ohm voice coil subs or the Infinity Kappa Perfect 12 VQ that is a single 4 ohm voice coil.  What would you suggest.  I currently have 2 Infinity 12 inch subs on these amps but would like to upgrade to the Variable Q Subs.  Which would be the best choice, the Dual Voice coil or the Single Voice Coil?

Although my amps are only stable at 4 ohms, could I run the dual voice coils in the parallel/series in order to get a 4 ohm load? If this can be done, what would happen? Would this cause the amp to put out less power or would this cause the subs to take less power?

I am contemplating installing 3 of the Infinity Subs to the 2 Rockford amps. If this is going to be an issue, I can get another 501s from my brother in-law for a song.

Thanks.