I am running two alpine type R 12s powered by 2 alpine mrd-m300 amps in the back of my hatch. Its not an overkill as long as you dont put the bass up too high. I was running 1 12 type R for a while there and decided i liked the two better. The bass is there when i want it and its clean (especially after i install my raammat60 next week!)
As for the JLs, in my opinion they make some of the best subwoofers on the market. But you really cant tell that by watching MTVs Cribs due to TVs higher kHz range of frequency (Subs are used for lower frequencies in the 10-100s of Hz). Monstas is what they are, listen to them in person.