Audio Systems: system upgrade, watts rms, watt rms

Question
I currently have a 99 s-10 ext. cab and am interested in a full system upgrade.  I already have a Kenwood 50x4 stereo installed, but the sound is poor and I want to upgrade the door and dash speakers as well as install a 12 inch Kenwood sub I already have.  What do you recomend in watts and brands for the speakers and what kind of amp (watts and channel, brand, cost effective) do I need to run the 600W sub.  I also am curious if you know how big the speakers are in the door and dash.  Thanks alot.  

Answer
I would nix the deck poweramps and use a 4 channel x 100 amp with a built in crossover.
While the deck says 50x4 it is actually more like like a poorly made, 35 watt RMS per channel amplifier with poor ventilation.
Peak power x .707 = RMS
RMS x 1.414 = Peak Power
I would always go with efficient Polk speakers for sattelites. They will sound great with 10-15 watts, while also being able to handle 150 or so, RMS [average].
Two of the 100 watts per channel =  about 50 watts RMS for each door [and dash] speaker.
The other two channels [when bridged to mono] will give you a solid 200 RMS for the sub (especially if the enclosure is properly tuned to the sub).

As to speaker sizes, go to www.crutchfield.com and follow their GUI for your specific vehicles info and requirements.
here is a direct link:

http://www.crutchfield.com/S-LQukTsys3D9/cgi-bin/autoinfo/autoinfo.asp?vehicleid...