The Radeon X1950 XTX comes equipped with 512MB of high-speed GDDR4 memory operating at a frequency of 1 GHz (2GHz effective) and not the GDDR3 o GDDR2 of the earlier models. With GDDR4, the  memory controller is able to  tap the high frequencies of the GDDR4 to improve performance of applications that needs extensive memory usage such as high AA/AF and high resolutions.

From the chart, we can see that the performance difference between a X1900XTX vs a X1950XTX. There is an almost 15% improvement in performance with the new X1950 XTX.