I would recommend between 32 and 35 psi cold for the stock tires as I have found the Z to be very sensitive to over inflation. With such a short wheelbase you'll notice that when you go too high on pressure the car will start to feel light and won't track straight at 70mph on the highway. It'll wander left, right, left, right, never straight. Also, the ride is greatly improved at 32/33 psi over 35/36 in my opinion.

As for aftermarket tires, it is complicated, but start with the stock recommended pressures and adjust down to get a more supple ride and increased straight line stability, and adjust up to get a more firm ride and increased turn in and responsiveness.

32 all the way around on my RE-11's.