I just replaced 6 stock Apple Hynix modules 2 GB (12 GB RAM) 2Rx8 with 6 Micron DDR3 PC-10600 2Rx4 (48 GB RAM) and all is working but their being shown as 1066 MHz. This is a Mac Pro 4,1 flashed to 5,1 on Mountain Lion 10.8.2 + supplementary fix. What I need to do to have 1333 MHz speed ? I've heard it might work with Nehalem CPU's or do I need Westmere ? http://arstechnica.com/apple/2011/0...nsform-a-2009-mac-pro-into-a-12-core-monster/ "Even if you didn't plan to upgrade the CPU, though, there are other benefits. Some Nehalem CPUs can support 1333MHz DRAM speeds, but are limited to 1066MHz on the older Mac Pros. The firmware update will enable the full 1333MHz speed if you have a CPU and RAM combo that can support it."