Maybe I'm wrong, I think my main assumption is that he would be using a larger box for porting it. I think that's the sticking point for me, and the error in my thinking.
The L7's can definitely take more power than it says on paper, but once the sub is ported and put in a larger box your taking it into your own hands.
The 15" L7 can take 1,000wrms all day long, but check around the forums for how many dissapointed users are waiting for their replacement subs after giving the same power in a large ported box.//content.invisioncic.com/y282845/emoticons/nono.gif.eca61d170185779e0921b0faa9704973.gif
If the 10's fit your setup, go for the 10's. Just adjust your gains accordingly.