The PowerColor HD 2600 Pro 512MB is on the losing side in 3DMark06, too. The gap is wider now at 308 points, and the value of each point is higher here than in 3DMark05.
The individual groups of tests do not allow to pinpoint the reason: it’s about 10% in both groups.
The first test of the SM2.0 group makes no difference between the two versions of Radeon HD 2600 Pro, but the second test agrees with 3DMark05 that the 512MB version is considerably faster. There’s nothing wrong about that since the second SM2.0 test is just a more complex modification of the second game test from 3DMark05.
The PowerColor card loses to the reference ATI Radeon HD 2600 Pro by 10% in both SM3.0/HDR tests. Thus, it is only in one test that the 512 megabytes of graphics memory give the PowerColor an advantage. For the other tests the memory frequency proves to be a more important factor.