Im laying the groundwork for a soho multitask server I am planning to implement within the next year. I will not have more than 2 or 3 simultaneous connections. Starting from the ground up the first component I am looking at the differences between AMD's FX series and Opteron series.
Looking at the current most expensive FX and comparing it to the cheapest Opteron price per cpu the FX wins as it has:
the same number of cores
roughly the twice clock frequency
Visualization and Hyper transport Technology
Smaller L2 and L3 cache
Alpha, you don't need a lot of processor power for a SOHO server. The server will not be overtaxed by 2-3 connections. You can, of course, overbuild a server, but in most SOHO environments the server merely serves as the housing and arbitrator for requests from the client. Being limited to two clients you can get by with a low end Llano or Celeron and save on the expense of both equipment and power requirements. I operate a home server with an i3 and it isn't overtaxed by 4 clients.
The reasoin that Opterons and Xenons are used in larger servvers is because they have multiple (10 + ) local clients and have to serve requests from many more clients remotely (if they are used by an enterprise). Usually the server CPUs are not built for speed, but parallel operations and reliability.
If your only choices are the Opteron and the FX, I'd go with the FX, because the Opteron in a SOHO setup is like killing a fly with a blunderbuss.