The biggest issue i see in all of this, is what some keep repeating, the box is too small... Now, i know more than enough to compare a Kicker CompC (from the late 90's) to an L7, but its what i have to work with. I had two CompC's in a 1.25cu per sub box (sealed) and it filled the entire back of my 90 Talon, i had to make struts to raise it to about a 35 degree angle so it would clear the strut towers. I hot rodded a shitty Radio Shack 170w amp and ran it at 2ohm mono and pulled 139.2 official, with a cassette tape in the stock deck. It did 148.x official with the windows down.
Id bet a decent amount of money that if you went with a single 12" L7 in a properly sized box and threw 1000w at it, you wouldnt be able to breathe. Something you never mentioned is how you have it wired up? At they single or dual VC? 4 or 2ohm?