Just for the record, that last backslash should be a slash. The correct link is here.
They mention a -3dB point of 34 Hz, which is the same as my previous crappy 8" Energy sub that I could lift with one hand. This is for the ForceField 3, not the 4, but given those measurement, and given the ForceField 4 is about the same price as the PB12, I think the choice is obvious. Mind you, I'm not saying the ForceFields are crap. But comparing GE's specs with hometheater.com's measurements, it certainly smells bad.
The rest of Warpdrive's comment is spot on. Yeah, if you can fit two PB12-NSDs in your budget, that would totally rock.
I am thinking that the pb12 will kick with my digm very well.