Xeon E6540 's Advantages
Higher specification of memory (1333 vs 3)
Larger L3 cache size (18MB vs 12MB)
Lower TDP (105W vs 130W)
Intel Xeon X5687 's Advantages
Released 11 months late
Higher base frequency (3.6GHz vs 2GHz)
More modern manufacturing process (32nm vs 45nm)