Agreed Henry.
I know that the XGT-Z is a superior hot, dry track tire to the MXX3 and the MXX3 appears better than the Sport. The XGT has better dry compounding, but carcass-wise, is an unforgiving tire for the average driver (as evidenced by the Club Slick deal where the casing was XGT-Z with stickier rubber). The MXX3 is far more consistent and driveable at the limit, but has a much lower temperature tolerance. I still haven't driven the Sports because I'm nursing the older tires along.