Originally Posted by veedubfreak
Except that ddr5 is NOT more than double the speed.
It's double the speed of GDDR3 at the same base frequency on the same bus width.
GDDR5 is the reason RV770 uses a 256-bit bus instead of a 512-bit bus.
i.e. GDDR5 does matter, because it allows them to use a smaller bus, therefore a smaller GPU, while still having enough memory bandwidth to feed the GPU.
Also, memory speed itself doesn't determine GPU speed. It's only necessary to have the video memory fast enough to saturate the GPU with instructions.
Although no memory controller or prefetching system is perfect, more speed is practically unnecessary past a certain point (that point depends on the GPU), and will only yield marginal if any gains.
The larger GPU itself, as well as the more traces needed on the PCB (because of the larger bus) make G200 cards significantly more expensive to make. Basically, RV770/790 can always be priced lower to give a better price/performance.