512 bit GDDR3 = 256 bit GDDR5that's b/c its GDDR3. Or about the same speed as GDDR5 in 256bit, which is still plenty fast. I wouldn't go as far to say that gpu is slow either. Its on par with a lot of current gpus in terms of memory bandwidth.
heh... rambus. they'd better be careful lest they get sued later.
so there's no need for 512 bit XDR2 either.