It would be nice to have a somewhat definitive list on what size wheels/offset work on flared & non-flared Zs (S30s in particular) with tire sizes.
I'm assuming you have flares or are you trying to stuff these wheels under stock sheet metal? I know the 18s kill ride quality compared to smaller wheels. The roads aren't too bad here in Oregon, but having some sidewall sure keeps the ride from being brutal.
It's interesting whenever I look at different brake setups & options, that the Billet 6 piston calipers are marketed as an upgrade over the the Forged 4 piston Superlites. I spent considerable time talking with the guys at Wilwood about that kind of stuff, as I was also under the impression that "bigger or more is better" and was planning on going with the 6 piston units. Anyway, I told them that I was building a street/track car and it would see some hard use and I wanted maximum braking performance. They recommended and sold me the Forged Superlite (4 piston) front & rear (different piston sizes f&R), telling me that the billet 6 piston actually have more flex than the forged unit and the billet calipers do not offer any performance advantage over the forged units. I like having matching calipers and found their info helpful. They also told me that slotted rotors are way to go and stay away from cross drilled, as they are only sold and made because people like the way they look. They'd prefer not to drill them, as all those holes do decrease maximum performance by cutting down on surface area. There is no doubt that when it comes to rotor size, there are benefits to bigger in regards to fade resistance.
Now, it's true that 95% of the guys out there will not work their brakes that hard and need that extra little bit, but I always maximize my vehicles' performance when I'm on the track....driving 10/10ths. Just thought I'd pass on that little tidbit from the guys at Wilwood that make these brake components. It's great that we have options and everyone has a different idea of how they want it to look, but this info is for those who are more extreme track drivers.