Of those two bikes Cannondale has more experience making better aluminum frames than Trek, and the Cannondale comes with the much highly regarded for reliability Shimano 105, not sure which Trek you were looking so not sure what it came with but the 1.5 comes with 105 so assuming that's it the Treks are heavier than the competitors.
However you can get a better deal from different manufactures like the Orbea Avant H30 that comes with 105 for about $200 less, as is the Fuji Roubaix 1.3
OR, if your not afraid of mail order, which is how most high end custom bikes are sold, but I digest, Bikes Direct has 2 great bikes in that same price price range that you're looking at. The FIRST is a titanium cross bike from Motobecane with 22 speed 105. A cross bike is much more versatile than a road bike with braze ons for fenders and racks on the rear which means you could use it for touring should you ever have the desire. It comes with 35mm tires but you could put narrower tires down to 32 maybe even 28 and you could go up to 38. See this:
Save Up to 60% Off Titanium Cyclocross Bicycles | Road Bikes - Motobecane Fantom Cross Team Titanium | Cross Bikes The SECOND bike is a ultralight carbon fiber bike made by Kestrel called the Talon, it come with Ultegra! It's a little bit more money than what your looking at by about $150 to $200, see:
Save Up to 60% Off Kestrel Talon Shimano 105 equipped Triathlon Bikes, Tri Bikes - 2011 Kestrel Talon Triathlon Tri Bikes The only problem with Bikes Direct is their customer service has slipped over the years, but for the price of what they sell their bikes for who cares? Of course you do have to partially assemble the bike when it comes, if you're not good at that sort of thing the most it will cost to have an LBS to assemble and check everything over would only cost you about $75 to maybe $100. And if you have a component failure within the 1 year warranty you just need your receipt and any LBS can handle the part swap but you would have to pay the labor...assuming Bikes Direct gave you the run around.
Anyway just some additional ideals.