Although AMD has only rolled out quad-core Phenoms so far, the folks over at German site PC Games Hardware claim they have benchmarked the yet-unreleased Phenom X3 and Phenom X2 processors - well, sort of. They actually use a 2.3GHz quad-core Phenom processor and shut down core by core to simulate dual- and triple-core parts.
The benchmarks only cover 3DMark06, Cinebench R10, and WinRAR, and compare dual-, triple-, and quad-core Phenoms clocked at 2.3GHz with an Athlon 64 X2 4400+ clocked at the same speed and a 2.4GHz Core 2 Quad Q6600. Overall, the benchmarks show the dual-core Phenom providing about 66% of the performance of a triple-core CPU, while the triple-core Phenom provides about 75% of the performance of a quad-core part. Check out PC Games Hardware's benchmarks here (translated from German using Google).