Just a late follow up, since I am on the Bimmerpost site again, but this time with a 2012 135i E88 Cabriolet M Sport dual turbo dual clutch that I just bought and... it is amazing.
Anyway, I saw this old post I had done in this forum and wanted everyone to know that my neighbor bought the Z4 from me and he and his wife love it and I get to still drive it occasionally