I don't think the Tarmac SL4 Sport is a good choice for you. Are you committed to going from flat bars to drop bars? If so , there are better choices, but honestly, the Coda you already own is better up to the task of carrying your weight than the Tarmac once the wheels are properly addressed. Ask the shop to stress relieve and properly tension the spokes.
If you want a different bike with drop bars, you might consider a touring bike like the Long Haul Trucker or Fuji Touring. They are built to carry a heavy load long distances.