I am currently running 17" wheels. I have run 20". I went back to the 17" because I didn't like the harshness of the ride with the 20's. They were wide too and seemed to want to wander when encountering cracks and things in the roadway. I loved the way they looked, but my X is a daily driver, so comfort one out.

Personal opinion: I don't like the look of super large rims with thin tires.