while the subs are nice, you DEF. shouldn't overpower them. They're SHALLOW subs, hence, SHALLOW enclosure. I think you be pushing them too hard. I also think if Kicker wanted you to give them that power, they'd have recommended it. Why not go with the 12"s, which could take the additional...
I'd personally go with 2 12" Kicker L5's (600 RMS each), but you'd have to build/buy another enclosure. They shouldn't run more than $300 for the pair. In my opinion, you should get a ported (vent style) box to increase output as well.