PC Gaming Hardware
in Germany has what appears to be the first ever Phenom X3 benchmarks, but what they've done is dissable one of the three cores on a Phenom X4 9600 clocked at 2.3GHz. This might be something close to what the real deal will perform like, but we'll just have to wait and see.
Their simulated X3 processor is faster than their 2.3GHz Athlon 64 X2 4400+ and another simulated processor, a Phenom X2 at 2.3GHz, which was the same Phenom X4 9600 but with two cores dissabled.
It didn't come close an Intel Q6600 that was also used for comparative testing and the benchmarks were limited to WinRAR, Cinebench R10 and 3DMark06's CPU test. As everyone has already guessed by now, three cores are faster than two, but not as fast as four, so there you are.
You can find the test results here