Good subs for loudness and a question?

Right now I have 4 polk db's with 720 rms a box both are vented one behind the other both going towards the trunk right now i have a bazooka monoblock giving 200rms and then a kicker giving 420rms and i just have ordered a hifonics super d mono it givies 900rms @ 2ohms and my friend is some how going to teach me how to get 900rms to each sub but I need to know do you guys think that buying two of these a href="http://www.onlinecarstereo.com/CarAudio/ProductDetail.aspx?ProductID=16275" rel="nofollow"http://www.onlinecarstereo.com/CarAudio/…/a kicker 15" l7s doing 1000rms a sub in one vented box will that knock a lot harder than the 4 12"s in 2 seprate boxes? The kickers are 4 ohms if i have that in one box can i get it down to 2 ohms? And then buy a amp that pushes 1200rms @ 2ohms? Or what do you guys think?