It's not conservative or not. JL rates their subs based on what power level will produce the best performance of that sub, with out sacrificing longevity.
If you want your subs to last a lifetime, and perform to their best ability, go by JL's recomended power chart.
That being said.... since SQ is not an issue with any JL subs (they will all produce great, smooth, tight sounding bass)...the number and size of subs you run will basically have an effect on SPL.
So, here is JL's chart that demonstrates how much air differenct size JL sub's push compared to each other. Two 13w6's will take 1000W continuous and push about the same ammount of air as one 13w7. The only difference by all accounts I've read, is that the W6's is a bit better sounding than the W7, but not by much.
That will be stupid loud, that's all i gotta say. I hit 144 db's on two 12's (W3v2) and a 500/1, so that should be sick loud.
Yeah I guess its just hard to make up my mind right now, Ive heard input from numerous ppl that the w6 sounds much better than the w7, I cant help but think that 2 13w6s would be louder/sound better than a single 13w7??