Though not many details were allowed to be disclosed, we do know that a new CPU corresponding to the current quad-core Core i7 875K (the K refers to an unlocked multiplier) was overclocked and tested running Cinebench R11.5. With only air cooling, the processor managed to run at 4.9GHz (Intel requested that the original speed of the CPU before overclocking not be disclosed), and apparently outperformed a 12-core AMD Opteron "by a pretty healthy chunk." Considering the Opteron in question easily beats a Core i7 960 CPU on the Cinebench benchmark, this is quite good news for Intel.
The second generation of Intel Core processors definitely looks impressive based on this single result (remember: this wasn't a pre-production chip), though we'll have to wait to get some independent benchmark scores before we can really see how much of a difference Sandy Bridge will make for the upcoming Core i3s, i5s, and i7s, overclocked or not. Expect the first evaluation processors to be benchmarked very soon!