If you browse the Mid-2012 Geekbench 4 results, you'll find that all of the highest scores have 2133MHz RAM inside of them. While this may likely just be coincidence that power users put in the best possible regardless of benefit, it does guarantee compatibility. Again, it stands that these systems can only address 1600MHz, and any faster will be slowed down (unless I am missing something). Might be a good experiment.