The factory wiring would be fine for the hi-po Panasonic. I'm running 90x2 RMS through it right now.
Ask dnewma04 (Dave) to build you a set of his "budget components" to replace the speaks in your front doors. I guarantee you'll be happy with them. I used them for an install and was quite impressed with them, especially the bass response.
I think the next most powerful HU's after the Panasonic are the mid-level Alpines which produce 26x4 (there's quite a few others in that range too). But, whatever HU you get, don't forget to bypass the factory amp.
