I've been researching this because I'm in line for a new GT4, so I (assume I) get to decide whether to go with PCCB or iron. It's true that most track rats, and even race teams, use steel rotors because of the price. However, there's a new generation of CCB that uses a different rotor material and sintered pads that folks are having great success with—at least so far. Racing Brake makes them, David Donohue raced them
, and others are trying them out. They seem to hit the sweet spot: lower cost and less fragile than PCCB, but with the same or better consistency, performance, and brake feel, and much better durability.
Also note that AP's new Essex-designed Radi-CAL iron setup is within 1.5 pounds per corner of the PCCBs, so they'd be a great option if CCBs are too pricey for ya, but you still want to ditch the extra unsprung weight.
I don't think either of these options available for the 718 yet, but are worth keeping an eye on. Since they're both aftermarket, I'm (again) leaning towards ordering the steel brakes on the GT4. The PCCBs are just too expensive for the benefits they provide given my intended use.