Tiagra is a big step up from sora in durability, and performance. Its a bigger step then from tiagra and 105. But the first question would be what do you want to use it for? Are you raceing because the cannondale with disc brakes can't be raced in UCI races. But if you arn't racing disc brakes are well worth the added weight in safety. If maintained they can stop you quicker then anything else in all conditions. Both the Trek and the Cannondales are great bikes and if you lose the sora, it really comes down to if you want discs or not.