ATI Radeon HD 4890 Overclocked Performance Tested
 

Let's jump right in and talk about GPU @ 1000MHz. Here's a look at what we get from

In non-CPU limited situations, the approximately 10% to 13% performance improvement out of a potential 17.6% improvement is nothing to sneeze at. Here's the break down of percent increase in performance at the different clock speeds we tested across three resolutions in all the games we tested.

http://www.anandtech.com/video/showdoc.aspx?i=3555