I had the opportunity to buy either the Elites or the SL's at near cost from the LBS. They overstocked on wheels while getting the race team they sponsor equipped. After checking on roadbikereview.com and a few other places, I bought the Elites and have not been dissappointed.
The Elites have a reputation for durability that the SL's lack. I race very little if at all so picking up that last tenth or two of a mph from the SL's just wasn't important to me. If I had bought the SL's, I would be doing 85% of my riding on my Cosmos and pulling out the SL's for special occasions. As things stand, I split time about 55/45 and get to have more fun on fast wheels.
The Elites have Hutchinson Carbon Comps for speed. The Cosmos are usually setup with 700x25 Michelin Carbons for bad roads, multi-day supported tours, and getting a better workout when riding/training with slower friends. I also use the Cosmos with Michelin Pro Race 700x23 for really hilly centuries, in between road conditions, or rides where I expect a lot of crosswinds.