2 18" Sundown NS or 2 18" FI BL's?

[tv559 0]

Ok now I need your guys unbiased opinion on which subs should I get. I will be getting a Sundown 3000D:). I have about 10-11 C.F to work with. Which combo will or has the potential to get louder? The BL's are less expensive but with the NS's I can always upgrade to another 3000D if I feel its not loud enough lol. Will the NS's be louder enough to compensate for the price difference? What do you guys think? This is what it will be going in below I will be taking the back seat out;)

Thanks,