On my '13 ZL1, I had my OEM wheels powder coated gloss black. It was this post on the Porsche forums from David Schardt at Forgeline that made me decide on powder coating over painting.
Powder coat if done correctly is a superior finish than paint. It resist chemicals, scratches and chipping far better than paint. If done correctly as well, it does not impact the strength or structure of the wheel. 100% of our racing team customers run powder coated wheels and love the durability and easy clean up of the finish.
On the other side of that, we powder coat all of our product in-house and have complete control of the process. If you take your wheels to a finisher that does not do wheels on a regular basis, then you take your chances. Stick with wheel finishers such as Wheel Medic here in Ohio or Wheels America who has locations all over the country.
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David Schardt
Forgeline Motorsports, LLC
3522 S. Kettering Blvd
Dayton Ohio 45439
http://www.forgeline.com
800-886-0093
http://www.facebook.com/#!/forgeline?ref=ts
My only caution going with a gloss finish is that it will readily show scratches and swirls in direct light.