OCC has published a review on the Sapphire HD 5870
A quote from the article:
>> Sapphire HD 5870 Review
I didn't think ATI had it in them to step up the performance on a video card this much in one fell swoop. The disappointing small jumps in performance from the 3 series to the 4 series are laid to rest with the massive performance increase over the previous ATI king of the single GPU hill, the HD4890. When you look at the performance you can tell that the level of performance delivered by the GTX285 was just a jumping off point for the performance expectations. After running the first bench with the Sapphire HD5870, the first thought in my head when I saw the result was "Damn, ATI is back." The Sapphire HD5870 even compared favorable to the dual GPU giants the HD4870x2 and the GTX295 in more than a few of the benchmarks.
>> Sapphire HD 5870 Review