Is dual opteron really worth it?

[Calcu]

I am going to build a new rig to edit and I need something that renders very quickly, so should I go with dual opterons, 3400+ or FX51? I know the difference between the 3400+ and the FX51 aren't really that much except for memory bandwidth but what I really want to know is if dual processors are worth the upgrade or should I go with 1 processor when it comes down to it? Also I was looking at the MSI K8T Master2-FAR, is it a decent mobo for dual opterons(~$220) or should I go with a AMD chipset for dual(+$400)?

Calcu