OCC has published a review on the Sapphire HD 5570 1GB

For the rest of us, overclocking is where it's at, and luckily in this regard, the 5570 doesn't disappoint. The overclocking potential is due to the GPU processor being built on a 40nm die that is easily cooled by the passive heatsink on the card. After some tweaking, I was able to adjust the core clock by 251MHz and the memory speeds were able to be increase by 200MHz. Once I reached these final overclocking speeds, the HD 5570 really started to perform better and in many instances it was equal to or just shy of its older (and more expensive) brother, the HD 5670.

Sapphire HD 5570 1GB Review