I'm also having this dilemma, though I haven't been looking at that many treks. Mostly comparing the Caad9-4 to say a Synapse Carbon 5. Still can't decide which one I like. I took both for a quick test ride and they didn't feel much different. Synapse was more upright, but supposedly the aluminum frame is supposed to be a little harsh? Like I said short test ride, I couldn't tell.