I moved from a very well sorted m3cs running Intrax 1k2, CSL arbs, CSL airbox, roof, bootlid etc. Brembo F/R BBK + rear seat delete.
to this MC
As you can tell I like Interlagos blue and the S54! My priorities are probably slightly different to yours but I would say having driven both 'out of the box' so to speak the M3 is indeed a more resolved handling and in particular riding machine, however the Z creates a far greater sense of occasion and to me speed/excitement. Of course you're comparing the convertible versions of both so there will be some differences, but as a toy (which it sounds yours might be) the Z definitely puts a pretty big grin on your face.