They get loud with less than that. If you want a SPL geared sub you should be looking at Mayhems or BTLs or the like. Yea Steve throws 7k at his, Trippi did the same, and that one dude with the Tahoe did 9k each... They all share the same stigma, high 50's. If you are out for numbers you shouldn't be looking at SMDs, but if you are out for a fantastic sounding sub (even with my wimpy 3kw each) you can't go wrong.
Yes I definatily want it to be loud, but I want it to sound great also, that's the main reason I chose the SMD!