The C3 Phenom II X2 555 Black Edition should arrive any time ....
Probably have a bit more 'headroom' than the C2 550.
The 6-core is supposed to be existing AM3-compatible ---- not sure about AM2+ backward compatibility (probably up to OEM BIOS writers).
It just a matter of time before AMD drops the AM2+ compatibility from the AM3 procs. It's been a nice ride, fer sure