Intel Xeon E5503 's Advantages
Lower TDP (80W vs 115W)
Intel Xeon E5 2665 's Advantages
Released 2 years late
Newer PCIe version (3 vs 2)
Higher base frequency (2.4GHz vs 2GHz)
Larger L3 cache size (20MB vs 4MB)
More modern manufacturing process (32nm vs 45nm)