As you can tell from the benchmark results the Palit GTX 560 Ti Sonic is faster than its reference-designed brethren, but lacks the raw power of the Zotac GTX 560 Ti AMP! edition's extra 50MHz clock speed.
The Zotac card represents the same boost over the Palit card as that Sonic edition does over the reference design.
What isn't shown here though is the performance of the competing Radeon cards, especially at the high-end, tessellation-heavy DirectX 11 benchmarks. The Nvidia and AMD cards trade blows across most of the suite, but the dual-tessellation engines of the Cayman GPU gives it the edge in the likes of Heaven 2.0 and with Metro 2033's tessellated character models.
DirectX 11 tessellation performance
DirectX 11 gaming performance