I have a 4,1 dual CPU model I have had for few years and have successfully repaired the tray due to a Northbridge heatsink failure. I feel a little more confident now. What is the fastest set of processors (quad cores) I can install in this unit without any modifications? I am not looking into flashing firmware into 5,1 or delidding at this time. I am looking for a simple swap. I see X5570 2.93 for about $65.