Intel Xeon X5660 's Advantages
Higher base frequency (2.8GHz vs 2.6GHz)
Lower TDP (95W vs 115W)
Intel Xeon E5 2689 's Advantages
Released 2 years late
Higher specification of memory (1600 vs 3)
Newer PCIe version (3 vs 2)
Larger L3 cache size (20MB vs 12MB)