There is a noticable difference going from my stock rims (21lbs) to my summer wheels (17lbs). Weight is what makes the difference in performance. The less weight the better. And remember, a 21lb 17" wheel will not perform as weel as a 21lb 15" wheel because the weight is further from the center of the wheel.
Bottom line, get the lightest wheel you can if you're at all interested in performance.
