In some cars, you can actually feel the difference but several things combined would aid in the performance gain. Like Bulldoger mentioned, the length does make a difference if you are changing out old, inferior wires made years ago compared to the latest design with near zero resistance. In theory, you would be able to open up the spark plug gap somewhat due to increased spark energy. In our cars, there is not enough spark travel even with average wires to realize a gain.

Steve