SQ = Sound QualitySPL = Sound Pressure Level (Loud)
SQL = Is a combination of the two. You want Sound Quality and Loudness at the same time. You will not have the best SQ, you will not have the best SPL but a nice mix of the two.
I do not think P2's are bad, but I think 1000 watts to them would be overkill. I also thinking paying retail for Rockford is kind of expensive....you could get a better subwoofer elsewhere for the same price or maybe less. If I were you, and your set on Rockford (I use RF...I like their amps) then I wouldnt get less then a P3 personally.
I bought 2 JL Audio 12w3's on Craigslist in a good sealed box for $100 and they are nice. The deals are out there, just take the time and do the research...
And if your like me and are unsure, ASK. The nice people around here will be happy to give their advice I am sure.