A small excerpt by James Weng from this forum (under a different name)
Each pipeline also can execute two multiple-add instructions in one cycle, twice the rate of the NV40. The end result is that one G70 can often outperform two 6800 Ultras in SLI.
Using SLI, the G70 is a different beast all together. At 1600 x 1200 with 4xAA and 8x anisotropic filtering thrown in for good measure, it managed to score an absurd 10611 3DMarks!
On its new MSAA
When creating game models, instead of describing each strand of wire on a chain linked fence as a dense mesh of triangles, game designers cheat by modelling such geometry as one large rectangle painted over with a wire pattern. What's not painted is encoded in the texture as “transparentâ€. While this technique spares the graphics card of excessive geometry calculations, when it comes to anti-aliasing, the GPU ignores such areas since MSAA only works on polygon edges. The new “transparent AA†mode in the G70 will find transparent textures and tag them to be anti-aliased using supersampling, which smoothes both geometry and textures.
And from 1up
based on tests run using the Unreal Engine 3's Engine CityStreet2 demo, a single GeForce 7800 GTX is faster than two 6800 Ultras running in SLI, by almost 30%