is it worth it????
 

ok so im in the middle of upgrading my whole system. It started with the head unit, i bought a pioneer AVH-x2600bt it comes with a built in amp (MOSFET 50 W x 4). next was the speakers i just bought 4 kicker ds 6x8s the rms is 50W peak200. Now I'm looking at the Kicker 12CX3004 CX300.4 amp its a 4 channel amp the rms power is 40 W x 4. Now is it even worth buying it and spend the extra 200 bucks or just save up and wait buy a KX800.5 Amp and the rms is 100W x 4.

General rule is always run as much power as you can afford to each speaker.
That way you will be able to have good output without blowing anything up due to clipping the signal.

A head unit that says 50x4 puts out usually around 22x4 rms wattage..and its dirty power no matter how good of head unit you have. You will notice a difference in sound for the better going from deck power (22x4) to an external amp that puts out 25x4. And thats not from the extra 3 watts per channel.

My vote is to run an external amp always. If you're on a tight budget you can always only amplify your front speakers since they are the most important and run the rears off of deck power. Then you would only need to buy a two channel amp which is much cheaper.