XPS 8960, Ram speed increase?

A DIMM with nominal speed of 5600 MHz will operate at a lower speed, typically 5200 MHz, depending on how many memory slots are being used. The speed of the DIMM is limited by the motherboard's memory controller.

For virtually everyone, more RAM is more beneficial than faster RAM.

First of all, the specs say "5600 MT/s memory is only available on computers with Intel Core 14th Gen processors."  But, it doesn't say that RAM will actually run at 5600 MT/s.

XPS 8960 doesn't have any XMP options for RAM speed in BIOS setup, so you probably won't get better than 5200.  There are threads saying some users can't even get 5200.