The Radeon HD 3870 will be the faster of the two, featuring a core frequency of 775MHz and 512MB of GDDR4 memory clocked at 1.2GHz. The lower-end Radeon HD 3850, on the other hand, will only feature 256MB of onboard GDDR3 running at 828MHz and a core frequency of 668MHz. Both cards will have a 256-bit memory interface, and support for DirectX 10.1 as well as PCI Express 2.0.
The information was accidentally (perhaps) posted on Diamondís website and promptly taken down, but the guys at TechConnect Magazine were quick enough to grab some screenshots of the company's product pages for the two cards. No word on pricing or availability, though.