More Specs Revealed from AMD Radeon HD 5800 Series
 

As you see, the HD 5850 will not have the whole 1600 stream processors and 80 TMUs of the HD 5870. AMD deactivates two of the 20 SIMD units of the HD 5850 to reduce the amount of stream processors to 1440 and the amount of TMUs to 72, which equals a 10 per cent reduction.
Additionally, the chip frequency turns out to be 725 instead of 825 MHz, so that it can only afford 79 per cent of the shader- and texture performance of the HD 5870.

http://www.hardware-infos.com/news.p...3188&sprache=1