I had an interesting conversation with Sal about Z2 vs. Z5. He said that different colors would benefit differently from Z5 & Z2 and that you really need to play with combinations of the two to find what's best for you.
(This is when we were discussing the new formulas, BTW)
Sal sent me one of each about the time they were released and I had applied one coat of Z2 and was about to apply another coat in preparation for a meet. I wanted it to look as shiny as possible, of course. I told Sal I had Silverstone (kindof a medium slate-gray metallic) and he really tried to push me towards Z5. I had always heard that Z2 is shinier and resisted, but he pushed me to apply the Z5. He said "If it was me, I'd apply the Z5". What's a boy to do?
What I did was draw an imaginary line down the middle of the car and apply a second coat of Z2 on one side and a coat of Z5 on the other. Then I took the car to the meet and challenged the other 350Z owners to tell me which side was shinier!
Guess what?
Everyone agreed (including myself) that the Z5 side was shiner and had a more optically-perfect reflection. Keep in mind that these are not good-old-boys saying "that shore is purty!" these are technical professionals comparing the sharpness of the edges in the reflections. The Z5 just looked better!
Now, I'm not telling you to throw away all your Z2. What I'm saying is that you should try different combinations of Z5 and Z2 to see what works best for you on your color and finish. We have always been told that a coat or two of Z5 mixed in with the coats of Z2 is beneficial. My experience proves that.