Carbon wheels won't necessarily save you weight, the carbon can allow for a deeper, optimal width rim for the same or slightly less weight. I just built my wife a set of wheels with 25mm wide rims that are 28mm deep which is really nice and only 445g. A carbon rim that is 25mm wide and the same weight might be more like 38-45mm deep so presumably more aero and stiffer or might be both more aero and a few grams lighter so saving an once or two. The result, depending on current wheel quality, you don't specify your hubs etc., means some weight savings, some aero advantage and possibly better hubs that will help you see some gains; though maybe not as great as you'd like. Helmet, clothing and position will help you see greater gains with position being the most significant. It doesn't mean that it isn't worth it to you; once ended up in second place by 2/10ths of a second on a 30 mile course after an hour and 20 min of racing. A minimal improvement of an extra 1/4 mile an hour meant the head of the pack might not have managed to catch me in the last few feet (I'd dumped the pack on an uphill 2 miles from the finish).