The framerate gains for the pre-overclocked memory (4100Mhz) and GPU (815Mhz) tally pretty well with the rise in component speeds over the stock GTX 580.
What's interesting is that, despite the higher speeds, there's no appreciable rise in noise.
Naturally the GPU and memory are generating more heat than the stock card, but the reference-design vapour-chamber cooler whisks away the extra heat with aplomb, and there's no audible difference between the Zotac GeForce GTX 580 AMP! and a vanilla GTX 580.
DirectX 11 tessellation performance:
DirectX 11 gaming performance:
DirectX 10 gaming performance: