Well GDDR6 isn't even ratified yet, so no way, GDDR5, as mentioned in the article, not based on the bandwidth # provided (was unlikely anyways).
However essentially a 200 Mhz (15%) boost for the shaders will help for sure, but how much depends on the apps. The truly shader limited stuff is still going to have a slight theoretical gulf between the two designs where the GTX280 is still below a single HD4870, although now just ahead of the HD4850; but overall I think this will help in games like Crysis and COD, however compared to the HD4870X2 it's still got a very loong way to go to match that on paper, and I think because it hasn't improved the memory, ROP and Texture situation that really the GTX280 will outperform where it currently significantly outperforms and will still underperform equally in the inverse situation, the area it will impact the most is in those where the two solutions are close, and there it will give the GTX a small bump.