New Guy,

The Kicker 700.5's 420 watts @ 2 Ohm is respectable power for a 10 or 12 in sub. You should have no trouble finding a 12 that will work in either a sealed or ported that will be a good match for that amp. If you want to stay in the kicker lineup, take a look at the 2011 L3 12". But since you already have a 10 L5, im not sure that you will really have a seat of the pants improvement going from a square 10 to a square 12 with the same amp wattage. Now going from a sealed 10 to a ported 12, I think you would see some difference.