One says "EXTREME" on the fenders and the other says "SUPERCHARGED" -- there are numerous cosmetic differences inside and out besides that, some of which are fairly subtle. Some of the more obvious are...
Extreme has 5-spoke forged wheels, while the SC has 7-spoke cast (5-spoke optional).
Extreme has a carbon fiber air splitter in front and diffuser back, while the SC has none.
the sleaker and more streamlined i think is the black car and the angles, i have an 06 extreme and my car says extreme on the side the only real differance in the cars is the 302 motor and the new intake sytem and the new bigger intercooler.