I was having the exact same dilemma as you and chose the sirrus sport '10 model. The sirrus was the lightest of the three bikes, though not that much lighter than the Trek. In the end, the ride, comfort, and weight of the three were very comparable, with the Trek and Sirrus being neck and neck, while the Cannondale was just slightly behind in comfort (didn't like the seat) and weight (slightly heavier than the other two). My final decision was based on color, honestly, as the dark blue of the Sirrus is really nice. However, the 7.3 fx is $500 now, so there is a significant cost savings over the Sirrus. Hope this helped.