I have a sentimental appreciation for Z4s as well but I don't think I would have described the Gr.3 Z4 in GTS as good! I naively picked it for a Manu series one time, tried real hard but figured that I was just too slow to get anywhere close to the top times. Then happened to try using a Lexus one time and realised that the problem might not be me...
I will never forget the time though that it somehow got me 4 straight wins in the rain at Spa at one of the rounds!
Weight distribution would be less of a factor if they had good setups at stock.