Benchmark Results: 3DMark 11 And Battlefield 3
When it comes to deconstructing the performance of a similar graphics architecture running at different frequencies, analysis is pretty simple. For example, the results in 3DMark 11 scale exactly as we'd expect in light of the shipping clock rates.
Bear in mind that Galaxy’s MDT x4 card runs at frequencies that are very close to Nvidia's reference specifications, so it serves as a reasonable baseline for GeForce GTX 560.
At Ultra detail settings, including 4x MSAA, all of these cards yield fairly playable performance at 1080p. There's only a 5 FPS spread between the slowest and fastest models.
Given an almost $40 range between the least and most expensive cards, you'll have to decide if features, bundles, and minor performance differences warrant the incremental premiums.