We've learned that GT200, the one we call Geforce GTX 200, does support GDDR5 memory, but you won't see a card based on it anytime soon.

It is quite reasonably because 1GB GDDR5 would cost a lot of money, and Nvidia simply doesn’t even have to try before ATI manages to get its R700 card out.

The second part of the story is that despite doubled bandwidth, that could jump to a whopping 300GB/s or even much more, and you wouldn't see much difference in performance. The question of whether it can be done is finally answered, but will it be done and if so, when, remain to be seen.