You're looking at about 0.1s per hundred pounds in the quarter mile. Besides removing the bumper beams, the heaviest parts are the doors, hood, and hatch (if you have one). All of these parts already exist in carbon. A carbon hatch is flimsy, and I wouldn't use carbon doors without a cage and serious door bars.

I lost 20 lbs by removing the stock springs/struts and adding JIC FLT-A1's.