Here is a chart of timings for a 6144K FFT on the i5-10600K.
The orange is
3200 14-14-14-34 memory and the yellow is
4000 18-19-19-39 memory.
We also tested the 560K FFT but as expected it was the same for both memory configurations.
We have already sold the i9 so we are unable to test it with the faster memory.