the Opteron and FX51's / FX' s - are indentical chips

as far as i can see - excetp the socket.
PS - do not buy a FX chip - since AMD has plan to change the socket in the comming months.
they are doing what intel did with the P4 - alot of people bought 423 and then they change to 478.
So if u can wait! and dont buy - heck, or even recommend an FX at this time - they are going to turn the FX into the budget chip i recall.