If you're interested in the overall performance of the wheel/tire combo you also need to consider overall inertia. Common thinking is that a light small (in diameter) wheel should perform better. That is true until you consider that the smaller a wheel you run the larger a (profile) tire you need (which places more weight further out). Thus you end up with a larger rotational inertia. For most wheels the difference between an 17" and 18" wheel is about 5lbs. This extra weight sits in the face rather than the rim (unless you also go for a wider wheel). I've yet to see people weigh tires to get a feel for how much the weight changes as you lower profile for a larger tire.
If you want style then get the wheel you think looks the best and don't worry about it. If you want performance it's hard to beat a Enkei RP0F1 17x8.5 up front and 17x9.5 in the rear.
"The 300ZX Turbo is a dance; it's a song; it's rolling, roaring automotive art. There is no color that doesn't suit it. There is no mood-lifting chemical substance it can't replace." - Automobile Magazine
