x2! i have not heard the rsd subs. but the Dayton H.O. is in the same price range. you won't find a better sounding sub for $115. they are very efficient when ported, and love very small boxes.Two Dayton Audio 10" HO's would be very good off 1200wRMS in both SQ and output.
My single 10 sounds awesome and shakes my tC quite a bit, I'm satisfied with the output. But if you put two in a 2 ft.^3 box tuned to 28-30Hz, it would be awesome!
They're only $115 each at Parts Express right now.
those are interesting indeed...I just found these today, CSS SDX10, $100 with VERY nice specs..http://www.audiojunkies.com/product/1040/css-sdx10-reviews