You also gotta factor in the size of your trunk opening. Your numbers mean nothing if you can't even get the box in the trunk unless you plan on building it inside the trunk.
no they're not missing the point. the point is different subs require different size enclosures. so yes they need to know what size your trunk is. what car it's going in, and alot of other factors, for the best help that anybody can give you.
Okay, since you don't want to consider electrical upgrades (other than big 3, I hope), then I recommend something efficient so that what you've got will take you as far as you can. For that, IDMax and Fi BTL N2 are good. The sound quality of both is reasonably good, especially for your type of music. IDMax is likely a little ahead on the SQ.