Hey Mark, my wife has an F30 335 and I have an E89 35i. Probably the closest thing right now to 435 vs. Z435
Long story story is that I think the F30 335 is the better car.
Cheaper to have/fuel/insure, better tech, similar straight line and handling when stock. (in the corners Z feels better because its lower but unclear if its actually achieving more mid corner speed)
EDIT: the 8 speed sport automatic is a very good gearbox that is a good approximation of a DCT. You should try it before writing it off.
Regardless of all that, Z435 is the car I WANT because I've always wanted a 2 seat sporty car (and I couldn't afford a Porsche...
)
I can forgive how easy it is to get too hot when driving hard, the lower fuel econ and the worse in-cabin tech because it is so much fun to drive around with the roof down. +30% power from a chip (if you are into that) because it is N54 (as opposed to +8% from N55) really adds to the fun factor