Go to a stereo shop and listen to whatever Pioneer (or whatever brand you think sounds good for the price Infinity, Alpine, etc.) speaker that fits your car in a 3-way or 4-way, you'll be happy. I went to Pioneer's site hoping to find the speakers they used to make with the compressed horn in them, they were loud, they didn't sound the best, but they did the job.
Just go ahead and get a coax, if you're planning on cranking them really loud and aren't planning on picking up a decent amp to amplify them properly, then there is no use in spending the money on a component set, they wouldn't sound right once you cranked them to the point of a distorted signal anyway.
Also, 80% is a good line to stop at when your listening to your music. Whenever you crank up the music to the point where you don't notice the voices getting any louder or they start to sound muddy and less crisp, cut it back a little. You aren't doing the speakers any good by clipping the signal like that, it just heats up the voice coils until it melts, sounds cool, but it isn't (except the cool crunching sound it makes when you move the cone after you take it out to replace it).
I think what I'm getting at, and sounding like a tool in the process, is that you should get whatever makes you happy and what sounds good to you, but I'd be a jackass if I thought I was original in that sentiment.
-Be cool.