With 8 cubes...which is probably max before wood, port and driver displacement...I say get 1 18", 6-7 cubes net on 2500-3000 watts and call it a day. You're gonna need to upgrade your alternator more likely than not and get another battery or two in the back. Never hurts to have more reserve power than necessary. It's easy to get louder than people in this state too because they think they're the shit. They think JL is the most ungodly loud stuff you'll ever hear. Get 1 18, build the box properly, give it good power and a solid electrical to keep up with the demand and you'll easily be one of the louder people in Seattle.