The Radeon HD 4870 and Radeon HD 4850 cards will both have a whopping 800 shaders. The previous generation had only 320 units, and as you can see we are now talking about more than double the number. ATI will market its cards as TeraScale engine capable and as we've suggested before RV770 will reach about one TeraFlop processing power. With 800 shader processors at 625MHz the Radeon HD 4850 can reach 1 TeraFlop, while the Radeon HD 4870 at 750MHz would reach 1.2 TeraFlop. People have reported that the card will end up with 480 shaders, but the number is bigger. Though it comes with a big amount of shaders these are generally clocked similar to the GPU frequency. - FudZilla

Radeon HD 4870 Features RV770 Having 800 Shaders

Now the big issue for ATI is that its 480 shaders might end up much slower than NVIDIA's technology which is featuring 240 stream processors. This was always the case in the past and NVIDIA's shaders are usually clocked at higher than GPU frequency. We believe that ATI's shaders were quite transistor cheap, as the RV770 die won't be much bigger compared to the previous RV670 and these numbers actually do bring some optimism. And it also is good in terms of heat reduction as a smaller die should give less heat, due to better optimizations, though ATI is always running quite hot in our opinion.

We also have some news that the Radeon HD 4870 will work at 750MHz. This is the final clock and we believe that most of the reference cards will work at this particular speed. This is a 25MHz slower speed than Radeon HD 3870 but the card will have more shaders and more raw performance. The slower of two, the Radeon HD 4850 will work at 625MHz compared to Radeon HD 3850 that works at 670MHz. This one also uses GDDR3 memory, while the Radeon HD 4870 uses GDDR5, both working with a 256-bit memory interface.