if you are looking to be competitive in an extreme class, id leave those DP's alone and step it up to the warden.,... how serious and how loud are you tryin to be? if you gonna run bout 1.5k to 2 21s vs a single sub on 4k id go the 21s.... you can easily do 150+db with 2 21s and 3k+ total power and keep it very listenable.... so answer this... whats the total power you plan on using.. and whats your final goal... overall loudness or strickly spl? youve got the airspace to play.... i personally did a 150.3 with 21 dps in my burb with bout 3500 to the pair and bout 16cubes... would been louder but the tuning was off....