This tire is definitely an improvement upon the already amazing Z1's. It is an especially good performer for the price. If you are looking a tire that is really grippy--one track or off--then this is a tire you will be impressed with. If you are looking for a tire with ride and noise comfort then look else where. This is a high performance tire and it has very stiff sidewalls.
I have gone through many sets of Z1's on and off track. I have yet to take these to the track, but from what I can see on the street I cannot wait.