Originally Posted by Dchiefransom

The only difference between Sora and STI shifters for that 7 speed would be that you can't "trim" the front derailleur on the Sora. Maybe you should go to a good LBS and ask them these questions. They can measure the dropouts and tell you for sure. When I put a new cassette on the back, the shop used an 8 speed chain for the 7 speed cassette. They said a 9 speed chain was too thin for the gear teeth.