That's what I was thinking too, it's "only" 210kg more though? Stats wise it doesn't look to make much difference, perhaps the big difference is from the old shape to the new rather than the coupe to the conv.
Fox, please let us know how different the Coupe feels after your test drive.
Housey, I know where you're coming from and I agree in parts but the main appeal to myself with the 3 over the Z is the extra room (as well as price, obviously). For someone of my stature the Z is too small for day-to-day but would be adequate for fun on a B-road. Have you found the hard-top convertibles "rattly, shakey, noisey"?