Prototype RV770 boards were clocked at about 1.05 GHz

The Radeon 4850 version is set to come to market with an 800+ MHz core (the final clock has not been specified yet and will not be available until the final qualification is completed), while the 4870 will be the first mass-production GPU with a clock speed higher than 1 GHz. Prototype RV770 boards were clocked at about 1.05 GHz.
http://www.tgdaily.com/content/view/37025/135/