According to AMD COO Dirk Meyer we can expect a significant number of new products from AMD in May and according to TG Daily this will include the Radeon HD 4800 series.
The clockspeeds of these new GPUs are still subject to change but the site says the Radeon HD 4870 will be clocked above 1GHz and the Radeon HD 4850 will have a frequency of about 800MHz. The chips will support both GDDR3 and GDDR5 memory and will feature 32 texture memory units (TMUs).
The new graphics card generation is expected to become available to system integrators and OEMs in GDDR3/GDDR5 variants with 256/512/1024 MB buffers. 256 MB GDDR3 cards are exclusively targeted at OEMs (as well as ODMs, Sis) and are unlikely to shop up in retail. Expect to see mainly 512 MB GDDR5 cards in retail for both the 4850 and 4870. Just like the GPU, the memory clock isn't set in stone either, but we were told that the GDDR5 memory is currently running at a physical clock of 1.8 - 2.2 GHz.
With a 256-bit memory controller, we're talking about 115 to 141 GB/s of bandwidth. This number equals the memory bandwidth record set by the 2900XT 1GB GDDR4 (512-bit interface with GDDR4 at 1.1 GHz DDR).
The desktop versions should arrive soon but the RV770-based FireGL workstation boards aren't expected until mid-August.