The stock radiator is a very wide tube single row high efficiency core. It is much easier to pull heat out of a single row core than multiple row cores. Some of the cheaper after market radiators that are double row have tubes that are half as wide as the stock single row and the core is low effciency. So between the double row that has tubes half as thick and the single row that has tubes twice as thick, the single row will be more effcient with the same type of fan. If one is wanting to use an electric fan, the stock radiator will work better. For road racing you can need more help, the biggest thing is to get more air through the radiator. Most people are putting more stuff in front of the radiator and hurting air flow. A bigger radiator will not help unless you can pull more heat from the radiator by allowing more air to get to the radiator. Also because the Z has a non-vented hood, the heat builds up in the engine bay. You really need a vented hood to road race to keep the temps down in hot weather. Road racing is extremely hard on Z32's because the oil temps get to high, as the oil temp increases, the metal parts receive more contact with each other. Oil starvation is also a huge issue.
