3 - Second base with R700
Both the 4850 and 4870 products utilize the same chip, make no mistake. What you'll notice is that the 4850 will run at a 625 clock frequency and comes with 512MB GDDR3 memory (framebuffer) clocked at 1986 MHz. These two factors are pretty much the biggest difference compared to the big brother 4870. Power requirements aren't bad either. You can expect a 110 Watt peak watt power consumption per GPU in this configuration.
That second configuration is obviously that sweet Radeon HD 4870. We see exactly the same GPU mounted on this board, yet there are some distinct differences to be found. The performance of this product is tweaked and maximized. You will notice that AMD's board partners will have higher clock frequencies on this product boosting out some more performance. Yet more importantly, this is the product you guys hear so many rumors about .. the product with GDDR5 memory. GDDR5 is a first for sure.
There are some distinct advantages to be found for GDDR5 memory. It's has much higher frequency based memory versus tight timings. In the end this gives the Radeon HD 4870 a performance boost as GDDR5 memory will leverage overall peak bandwidth to a theoretical (roughly) 3.6 Gbps. And that's just crazy fast (GDDR3 on 4850 = 2.0 Gbps).
This is the biggest difference between the two (4850/4870) models. Next to the memory, and I already mentioned this, you can expect higher clock frequency for the core/shader domain, 750 MHz will be the default clock frequency and memory wise ... the frequency sees 3600 MHz.