I can only compare with motorcycles, but if the analogy holds a better car will not automatically mean better laptimes. Well, i mean, significantly better laptimes. Now ok, if you were going from a Ford Ka to the Gallardo this will have an influence, and a HUGE one, but its not like the 350Z is some kind of old crappy vehicle.
I guess you will be faster but not with a huge margin, for the reasons you stated yourself. If your car can brake later, and corner faster, its still the nut connecting the seat and the steering wheel that has to do it