Much higher than 1GHz
AMD is playing with the idea of a faster Radeon HD 7970 chip, that would probably end up with a new brand, if not only Radeon HD 7970 OC edition.
The chip can easily go over 1000MHz and some products in closer to 1200MHz are also possible and AMD is thinking about doing it. Several things indicate that the company is working on a faster version and second wave of overclocking products, but it has not been decided when and at what speed and brand they come out.
AMD graphics partners will make their own overclocking cards, but at a later date when AMD gives them the green light. AMD could time the launch to compete with Nvidia’s Kepler when it comes out. We will keep our eyes open for new products but the usual overclocking suspects are working on 1000MHz+ Radeon HD 7970 cards as we speak.