As usual the leak comes from Chinese website Pcinlife.com. There we see an image of a 3DMark Vantage score paired with a GPU-Z screen shot. There are plenty methods to Photoshop images such as this, but with GPU-Z being included in the image, it does give some validation to the source.
If the post is to be believed, the AMD HD 6870 scored a total of 11,634, which places it well beyond the current HD 5870. In our internal testing the average HD 5870 score is just over 9000 (!!!). So, if the score is accurate we could be looking at a sustainable performance increase from the 5000 to 6000 series of graphics cards.
The site ran additional benchmarks to gauge the performance of the card. With Crysis on very high settings at 1920x1200 pixels with AA set to x4, the HD 6870 was rumored to run at an average of 43.55 frames-per-second. Unigine -- which tests DX11 and tessellation performance -- the graphics card was said to average 36.6 FPS, even with tessellation set to extreme.
These benchmarks are a good showing for the upcoming AMD 6000 series graphics cards, however, we have no way to verify the authenticity of the results.