You should try to ride the bikes on a road and not a parking lot. Once on the road be sure to get into a riding position with your hands in the drops and on the hoods. Do some accelarations, turns and braking with the bike at speed. You want to get the feel of how the bike will work for you while riding at normal speed. Sitting up and riding around a parking lot at 10 mph is no way to test out a bike. The LBS should be able to put you in the right sized bike and make it fit you. The all carbon bike will be a little more comfortable on long rides. Componets on both bikes will be good as they are not cheap bikes. If the bikes have Shimano 105's or Ultrega you'll be fine for years. Think about when you might be getting your next bike, if its soon then go with the cheaper bike. If you plan to put several thousand miles a year on the bike, race it, and intend to keep it for 4 or 5 years then get the more expensive bike. Which ever bike you choose, be satisfied with it, and don't look back on your decision.