The site claims the the R680 will have a similar frequency to that of the upcoming Radeon HD 3870, so probably around 775MHz. The card will have the same height as the current high-end cards but will be longer and will feature a big cooling solution like the Radeon HD 2900 cards.
The launch date isn't settled yet, it may be January but it could also be early February - and that's if AMD manages to get the chip ready in time.