the first site out with benchmarks of AMD's new Barcelona core and they've done exactly what AMD didn't want, they've used a Barcelona server to simulate Phenom X4 performance.
The server had its PCIe riser card removed and a GeForce 8800GTX put in its place to allow for some graphics intensive tests to be run.
This might not be the ideal way of doing things and the Opteron 2350 processor used was only clocked at 2GHz. AnandTech also managed to get hold of a 2.5GHz CPU and compared it against the 2GHz one.
The test results aren't overwhelming, but bear in mind that these numbers are only indicative of what the Phenom performance will be like as the motherboard used isn't designed for mainstream application performance and it only had DDR2 667 memory.
You can read the entire preview here