Probably the best "comfortable" performance shoe on the market. I've not tried the clay version, but I suspect it performs equally well to the hard court version. In fact, I've played on clay with the hard court version and the shoe performs quite well.
The only down side is durability. My latest pair of GR2's has 40 hours on them and I've nearly worn a hole in the toe of my right foot. The most I get out of them on hard courts is 80 hours.