I had a set of OZ wheels on my first Porsche, a '87 930. Great looking wheels but the person who bought it went back to the stock Fuchs. My last Viper had HREs, which are real nice but cost alot and most, if not all, are 3 piece, which based on my experience, can be troublesome after extended periods of heat (i.e., track time).
Take a look at Tire Rack & Discount Tire to get some ideas and as others have said, ebay is a good place to buy from as long as you know what you want.
Porsche Panny 4S
Hybrid Mode
