Your Mac Pro has 8 slots and the maximum possible upgrade is 128GB (8x16GB). Kit Capacity: 128GB. The 8 Core model the Ram will only run @ 1066Mhz. If however you were to upgrade and install a CPU that was capable of running 1333Mhz ram, the ram would then run at 1333Mhz, its a very useful dormant feature that you can enable in the future when upgrading your CPU.
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