Oh,
Post a photo of your Cannondale Supersix.
What is the handlebar position? Spacers? Stem angle?
Lowering the handlebars to the lowest possible level could potentially do more for you than a whole new bike.
Think Aero positioning of your body.
How are your gears? Topping out on the high end?
A speedometer can be handy for training and pacing yourself. Cadence? Power? Heart Rate?
How is your "race" held? In particular with drafting? Hold the pocket behind your nephew for the whole race, and then all you need to do is out sprint your nephew on the last few hundred yards. Of course, he'll figure that one out quickly (if he hasn't already).