What I want to know is, where did you get this
<< I know that it is a AMD big selling point in many cases and is claimed to make your system run twice as fast. >>
idea?
I've NEVER heard anyone, most especially not AMD, but not even the most raving ddr lunatic, make this claim. I've only heard this from people asking, "sniff, why doesn't 2x as much memory bandwidth give 2x as much performance?". I think the answer is the same answer to why Rambus didn't rule the world, and it didn't have everything to do with latency (tho that is part of it).
The biggest thing is, that today's apps aren't as voracious for bandwidth as you might think. In a few years, who knows, but otherwise...