I currently have a 2011 Trek 1.2 (Tiagra/Sora) and I'm seriously thinking about upgrading my derailleurs. I've seen a lot of pretty good deals on ebay on Ultegra components, but I noticed that the rear derailleur is for bikes with 10 speeds. Will this work if i only have 9? If not, does this mean i have to upgrade my cassette as well? I really only want to upgrade my derailleurs for now... with that said, what are my options? Thanks in advance for the help guys!