The Tech Report translated some benchmark results from Chinese website HKEPC. They got their hands on some of the upcoming Core 2 Duo processors with a 1333MHz front side bus.
In its evaluation, HKEPC benchmarks the E6850 (3GHz) and E6750 (2.66GHz) models in a variety of apps including Cinebench 9.5, DivX 6.2, LAME, PCMark 2005, WinRAR, Battlefield 2142, and Doom 3. The Core 2 Duo E6850 has a definite edge over the existing Core 2 Extreme X6800, but it does also have a slightly higher clock speed (3GHz vs. 2.93GHz). At the same speed, the faster front-side bus seems to matter less. According to HKEPC's tests, the 2.66GHz Core 2 Duo E6750 is only 1.38% faster on average than the 2.66GHz Core 2 Duo E6700. Some real-world apps, like Far Cry, give the E6750 a slightly bigger lead, but there seem to be few major differences between the two chips outside of some synthetic tests.