ATI plans to use GDDR5 memory on its R700 and RV770 graphics cards, according to FUD Zilla.
It looks that GDDR4 didn't really hit off well, as it doesn’t brings a lot of advantages over GDDR3, but GDDR5 promises some crazy frequencies all the way up to 2.5GHz / 5GHz effectively, which is more than two times faster with what you can achieve today with GDDR4.
This mean that the new memory will have more bandwidth and this is something that graphic card always enjoys.