Seems that the photo of the R600XTX that made the rounds on the internets last week was the design that Apple (& Apple alone) is adopting. The card will also ship with an "Overdrive Zone" available in the Catalyst Control Center drivers, but only if you power it right. From the Inq:

"Yes, you've read it right - the R600XTX is coming out with a legal overclocking mode, no nonsense and limiting overclocking to its partners like some other companies have. The clocks have not been set yet. Even AMD is waiting until a couple of days before the launch before it makes that decision."