Yesterday I successfully completed my 3rd MP4,1 to 5,1 upgrade. This one took longer than I expected as I ran into a weird issue having the CPU B recognize the new memory. The originally MP4,1 was an 8 core at 2.93 GHz with 32 GB RAM (8 x 4GB modules at 1066 MHz), spinner for boot and a very old ATI 4870. The new MP5,1 was equipped with 1) 2x X5680 processors (12 core at 3.33 GHz, TDP/procssor at 130 watts) 2) OWC's 480 GB PCIe SSD for booting + Apps (providing 680 MB/s) 3) 2x 3G SSDs in Bays 2&3 and setup as RAID-0 (providing 520 MB/s) 4) Nvidia Quadro K5000 (drawing a max of 122 watts) 5) 2TB spinner in Bay 4 for Time Machine 6) 1TB spinner in Bay 1 for cloning the boot PCIe SSD The original Geekbench 3 (64-bit) score was for single core 2347 and multi core was 18427. The final scores were single core 2714 and multi core was 30745. We have a MP6,1 (fully pimped out with 12 cores, 2.7GHz, Dual D700s, !TB SSD and 64GB RAM) and its Geekbench 3 (64-bit) multi core score is at around 33000. The system boots up in 16 seconds (Startup chime to the Login panel) The new MP5,1 upgrade cost around $4000 (the largest chunk being $1600 for the K5000). The pimped out MP6,1 cost around $9600. The K5000 is extremely quiet when under load (no fan noise could be heard at all). This is in contrast to the Sapphire Radeon HD 7950 (installed in another office MP5,1) which becomes very noisy when under load. I encountered an issue after replacing the CPU B with the new X5680 processor. At first the two of the small 8 red LEDS between the heat sinks lit up as soon as the system was booted and the system was complaining the new RAM (8 x 8GB modules) was incorrectly placed and that the slot 5 had no RAM in it. The display suggested the correct RAM module placement, so I at first thought maybe one or more of the RAM modules were faulty. The system also suggest I try using "/System/Library/CoreServices/Memory Slot Utility". I went around in circles for maybe 2 hours trying to figure out what was wrong. I even reinstalled the original RAM (8 x 4GB modules at 1066MHz) as I knew that was good, but still encountered the same issue with the system complaining about the memory. I knew that if any of the small red LEDs lit up they indicated that one of the CPUs was having issues addressing/seeing memory. The red LEDs that lit up were closer to CPU B so my assumption was that my installation of the new CPU B was causing the problem. I removed CPU B and checked every thing, removed the X5680 and reapplied new thermal paste and ensured it was seated and aligned correctly and proceeded to then bolt down the heat sink with utmost care tightening the bolts correctly and in the proper sequence. Much to my delight, this did the trick and all memory was now being discovered correctly and no red LED was lighting up. I should also mention that when launching and executing the Firmware Update Tool before starting the upgrade it would halt saying the internet wasn't accessible. This confused me no end as my browser was able to do so. After much ado fiddling around, the office IT person was called in and it was discovered that the Firmware Tool actually performs a 'ping' to its server out there in Cyberland to make sure it can communicate with the server for download the appropriate firmware related info. As the office had a Firewall configured the IT person indicated it would block out going 'pings'. Once this was figured and with the Firewall configured to allow outgoing 'pings' temporarily all went well and the Firmware Tool was happy to proceed without issues. What should have taken 4 hours ended up taking me close to 9 hours. I left the MP5,1 running the Geekbench 3 (64-bit) stress test for 'ever' so will see how the new system is come Monday morning.