DailyTech published some snips about the upcoming Radeon HD 3800 series graphics cards:
The lower-end Radeon HD 3850 will only feature 256MB of onboard GDDR3 running at 825 MHz, and a core frequency of at least 660 MHz.
Higher-end Radeon HD 3870 will feature GDDR4 instead of GDDR3 while using the same RV670 core found on HD 3850. This GDDR4 memory is clocked at 1.2 GHz, and the core frequency is bumped to 775 MHz. The GDDR3 version of HD 3870 will feature the same core frequency as the GDDR4 card, but comes standard with lower frequency GDDR3 instead of GDDR4 to target a better price point.
The red flag is that Radeon HD 3850 touts exactly the same features found on the 80nm Radeon HD 2900 design with the exception of reduced GDDR3 memory. HD 3850 will reduce the thermal envelope when compared to the previous generation, but performance should be nearly identical to Radeon HD 2900.
Radeon HD 3870, on the other hand, is an ambitious bump from the older generation. The 775 MHz core frequency represents more than a 100 MHz increase, while the memory receives a 400 MHz gift over R600's GDDR4 implementation.
A memo circulated from ATI design teams to third-party vendors indicated that vendors will have the ability to set memory and core clock frequencies independently, so each vendor's card will perform at slightly different frequencies.