I've been running 2 JBL P1222's on a 1201.1 for a few years now, I have had them in a 3.5 cube box and an 8 cube box respectively, I've never a/b them but they seem to have more impact than a comparably priced type R... I'm also running the power 6.5 components and have had reasonable success with their sound

 

how is that 8 cube box? that more than twice the recommendation of jbl.
would you notice much of a difference to the gti?

 

Mach5audio gets my vote, great price, product and canadian. Not to mention a very low fs in all there subs.

 

Fi Q is a great budget sub that sounds amazing and gets decently loud. I happen to have one used in great condition but thats not why I suggest this sub. The new ones are supposedly even better, just came out in april.