Two of my buddies have Paradigm subs (one has the PDR-10 and the other has a DSP-3400).
Both sound fantastic, though are quite different animals. The PDR-10 was punchy and musical (reminded me on an Energy sub, actually), while the 3400 made my molars rattle and jellified my intestines during a movie. This was in a room with hardwood floors, approx 15 x 20, and my buddy said he had the sub turned down pretty far.
I've heard great things about the SVS stuff, but have never heard a unit so I can't compare. This being said, I can't picture how anyone could be unhappy with a 3400. It is one serious subwoofer.
Hey you can save even more money! Keep your CF 50's. My buddy with the 3400 has Monitor 9's and I admit I am a bit underwhelmed in the value-price for these speakers.
H/K AVR 1600, SD RTS-P100, Mission 670i, Paradigm C-200, CV Sub-120, Shaw Direct 630, LG 50" Plasma, PS2, PS3