I have not ridden any of the Flying Dutchmen coasters such as X-flight, but My mom and I rode Superman at SFOG last year, and it was by far the smoothest Roller Coaster that my mom and I had ever ridden, and a nice exciting ride. The only downside was the ride kept breaking down so we waited for about an hour and a half to ride it, it was well worth the wait. Having stated how smooth it was I really hope that X-flight is more intense and just as smooth. Still to this day, the five smoothest coasters that Ive ever ridden are Superman, Montu, Kumba, Rockin' Rollercoaster at MGM, and Mindbender! what about you all?