purchase 10's or 12's

i have never heard  the kappas, but i do know that alpine's slam and sound good doing it.  My co worker has 2 R-10s in a ported box tuned to 30hz i believe, with a alpine mrd-m1000 running them in a mazda b2200 extended cab.  belive it or not he can hit 145 db.  He broke our mic in the process, now i can't test my 3 R-12"s with 3 mrd-m500's.

Now for the sound quality, our team car has 2 R-15's, and they are unbelievably crisp for 15's, they sound like 12"s, but with the output of 15's.  And the 12's sound like 10's, and so on.  but then again it really depends on the box.

I also like the voice coil options of the R-series subs, you can get dual 2 ohm or dual 4 ohm.  if your amp is stable to 1 ohm, then go for 2 swr-1241d's.