Do you need such a small form factor? For your price range you could get the PB12-NSD
, which will give you more output thanks to the larger box and vented design, digs to below 20HZ, and will outgun the SB12-NSD, the Sunfire and your Klipsch by a decent margin.
Another sub to consider, if you could swing the size, is the Hsu VTF3 MKIV
. In black, after shipping, it is about the same price as the PB12-NSD, and offers similar performance.
Basically, what kini62 said above.
Both are pretty darn good subs. They both also come from companies with excellent customer service, product reliability, and have good warranties and resale value (which are other items one should consider IMHO).