People are paying through the nose for 939 chips like the good ol FX-60. Users that buy such CPUs often have a fairly decent SLI or crossfire rig that is held back by a single core CPU, or they fried theirs overclocking it.
Anyway you will see a gain upgrading to a 550 BE, but you will realize a larger gain when you overclock it of course
. With the money you can make selling your old S939 board and CPU, they really are worth more apart than together, you may even be able to spring for a quad core Phenom II.