Performance in Synthetic Benchmarks
3DMark06 defaults to 1280x1024 without full-screen antialiasing, so it is normal that the overclocked Gainward HD 4850 1024MB GS is but slightly slower than the Radeon HD 4870 1GB. The gap was wider in individual tests, especially in the SM3.0/HDR tests that are more sensitive to graphics memory bandwidth (up to 664 points).
Futuremark 3DMark Vantage
We minimize the CPU’s influence by using the Extreme profile (1920x1200, 4x FSAA and anisotropic filtering). We also publish the results of the individual tests across all display resolutions to provide a full picture.
Despite the high resolution and antialiasing, the Gainward HD 4850 1024MB GS with a memory frequency of 1200 (2400) MHz is about as fast as the Radeon HD 4870 1GB with GDDR5 clocked at 3600MHz. The difference is a mere 245-265 points, which is too little for such a significant difference in memory bandwidth. Thus, the performance of RV770-based cards is limited by some other factors in 3DMark Vantage.
It is when both the GPU and memory are overclocked that we have the biggest effect in the first test. The Gainward is almost as fast as the Radeon HD 4870 1GB, the smallest gap being at 1920x1200. The factory overclocking is not rewarding, increasing the average frame rate by no more than 1fps.
The second test shows pretty similar picture with that only difference that the overclocked Gainward card falls farther behind Radeon HD 4870 1GB in 1280x1024 resolution.