How much can you get a TCR Advanced Pro for? I would choose that over the Propel SL0. Lighter, stiffer, cheaper, better handling, better brakes. Just more enjoyable to ride. Also you don't get blown around as much in the wind. Only thing going for the Propel is the aero which doesn't make much difference unless you are riding time trials or racing where you think the last little bit of speed might help. And it is only a small amount. I haven't had a Defy but do have Propel SL0 and a TCR SL0 and TCR SLR.
Also remember the Propel is now an old model with the completely new one is on the verge of coming out. Obviously the reason they are trying to do a deal on it.