Even on older cards people have been seeing a huge increase in performance. But even if this only improves the Xbox One 20-30% (which is less than half some of the older cards are getting). It's still not that noticeable.
It will be nice to see what it does. Some of the demos were rather impressive. Look at first gen Xbox 360 to the very end - say the new Tomb Raider or Halo 4.







