Intel Xeon E5507 's Advantages
Higher base frequency (2.266GHz vs 2.2GHz)
Lower TDP (80W vs 95W)
Intel Xeon E5 2660 's Advantages
Released 2 years late
Newer PCIe version (3 vs 2)
Larger L3 cache size (20MB vs 4MB)
More modern manufacturing process (32nm vs 45nm)