Unless you're really desperate to save all the weight you can or are riding Campy I would go with the Pro over the SL. They just upgraded the Pro model so that it looks exactly like the SL, has the upgraded bearing and seals of the SL, and has a steel cassette body instead of the SL's aluminum. The steel cassette body is nice because 10sp cassettes don't eat into it the way they do into aluminum cassette bodies. Plus, it's $300 cheaper. Also, if you're going to get a front wheel to go with it consider the matching hub. I kind of got forced into buying one and thought it was going to be crappy, but was pleasantly surprised by it. The hub is close in quality to a Record hub.