So i can get two pairs (4) 6.5" coaxils and run them off an amp in my truck, or a set (2) component speakers. Which will get louder and sound better. The 6.5's will be about $150 a set Comps. will be about $300 a set
Well there is a big difference in a component set and co-ax speakers. Co-ax are suppose to be direct drop in replacements. Since you would be running 2 sets your amplifier would see a 2ohm load ( if your amp is 2 ohm stable and the speakers are 4 ohm) So you would push more power to them, Than a single set of 4 ohm components. They are also quick and simple to install.
On the other hand a single set of components typical handle more power and allow the placement of the tweeters for the best sound stage possible.
In short if you just want loud and aren't worried about sound quality go with the co-ax's. If you want you music to sound, the way you want it to sound buy components.