Your body weight will impact your performance in endurance events!!!! The longer the event, the bigger impact it will make. Carrying an extra 10 pounds over a 4, 5, or 6 hour race will definitely slow you down. This is especially true for runners and cyclists.
If you want to see big gains in your racing, make a serious effort to drop any excess weight you are carrying. Do this in the off season when you are not doing high intensity workouts. Keep the weight loss gradual over time. Assuming you do this in a healthy manner and at the right time of the season, you will be faster. Give it a shot and see what happens.
Here is a cool calculator that will predict how your body weight can impact your running performance. I have found this to be fairly accurate
http://www.runningforfitness.org/calc/weighteffect.php