As far as I can tell, they both have 105 11 speed. I would buy the carbon over the aluminum for a difference of 50 bucks. It is going to be the base entry level carbon for Trek, so it won't be as nice as the SL, but it will overall feel nicer than aluminum.
I would think the build spec is near identical on the two bikes given that they are both 105 builds. Where are you getting your weight information?