Which is fastest memory configuration: 2X8 (16) or 4X4 (16)?

Is there a speed advantage with one memory configuration or another?

The PC in question has four available memory slots.

In terms of sped you won't see a difference. This goes for the RAM speed its self. Don't think for a moment 2800 is better than 1600. Unless raw RAM speed is needed for your application, you will NOT see a difference in performance. So in a nutshell, save your money and by the slower stuff.

To answer your question, you'd want to go with the less equals more philosophy. So 2 x 8. Each configuration you list still uses dual channel...

If you have that RAM laying around you could always test the numbers. Command line that tests RAM speeds.

But that may be for the chip its self.

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Do you even game and use above 12 GB?

No.
Just non-Gaming stuff.
Was interested in how to best populate the memory slots for the best performance without using a microscope.
I guess just using 4X4 will be the less costly vs 2X8 without any performance loss.

Thank you for your feedback.