As said before, lighter wheels will make the biggest difference.Those 719's are heavy and bullet proof, probably use 36 spokes, and are built for superior strength. That is what I built my touring wheels with. Putting on some light weight wheels would lead to better acceleration, but more work on keeping them rolling.
My experience with bike weight has been minor. I ride a 16.5lb road bike for weekend rides and a 35lb touring bike for commuting and touring. Cruising speed is about the same if I am alone, I might roll a bit faster on the carbon bike, but it doesn't have a computer to give definitive info. It definitely accelerates much faster and is more nimble, but the heavy bike is more comfortable.
Given that group rides are a long series of accelerations over varied terrain, I would suspect that my light bike would cause less fatigue over the ride due to less effort needed to accelerate multiple times over the ride.