The best thing is the clock claim where ATI hopes to get the final chip at a frequency higher than 700MHz. At this point people don't know the exact frequency as the final silicon is still not out but the estimation targets at more than 700MHz.
This chip is 80 nanometre and scheduled for January/February time. To try to be more corporate precise you should be able to buy one in Q1 2007 and it will probably come shortly after Vista. ATI will struggle to launch it as soon as they have enough cards ready in production.
It still looks that G80 will be the first next generation chip on market. µ