Depends on what you're using the server for. One of the machines I manage is a dell poweredge with an E3-1220 (Sandy Bridge) and it is used for DNS, DHCP, Running wifi APs, file server and a backup server for about 10-15 clients at a given time. For those tasks the difference would be neglible and the CPU is never strained. But if you're using it as a workstation or rendering farm I could see where there would be some benefit. But if you were using it for that you probably wouldn't be looking at an E3