Some details, albeit completely unconfirmed, on AMDs upcoming Radeon HD 8800 series have surfaced on the web. The Sea islands HD 8800 series apparently is based on a new silicon codenamed "Oland," which is made using a  28 nm process while packing 3.4 billion transistors all on a 270 mm² die-area. 

The Radeon HD 8870 would be clocked at 1050 MHz with 1100 MHz PowerTune Boost frequency; while the HD 8850 is clocked at 925 MHz with 975 MHz boost frequency. The memory of both SKUs is clocked at 6.00 GHz, yielding 192 GB/s memory bandwidth. The chips hence have 256-bit wide memory interfaces. Sources Videocardz and Read2Ch claim there will be two HD 8800 series models which typically is a Pro and XT SKU. The source mentions that the HD 8870 provides up to 75% higher single-precision floating point and up to 60% higher double-precision floating point performance over the the HD 7870. The texture fill-rate should be up by 65%. The Radeon HD 8850 offers similar increases over its predecessor, the HD 7850. Check out the table below.