I come to leave my contribution.
I tried in any way to operate with Infinity Fabric at 1900mhz, but it was not possible.
The Asus X570-E STRIX bios does not have the visible adjustment "SB spread spectrum".
However, with the AMIBCP program, I could verify that it is in bios 1407, but disabled.
I managed to edit the bios, but when saving the modified bios it loses the "capsule signature".
And both ezflash and biosflashback do not accept bios without "capsule subscription".
Looking in a forum I found a modified bios 1405 that had the setting "SB spread spectrum".
However I wanted to use bios 1407.
Here comes the trick!
I installed the modified 1405 bios, deactivated the "sb spread spectrum" in this bios and created a bios profile and saved it to a USB stick.
That done, I installed the latest original 1407 bios and ordered the profile reading saved from the modified 1405 with the sb spread spectrum setting disabled.
To my surprise it worked !!!
Although the spread spectrum adjustment is hidden, it is DISABLED!
I now have 99.98mhz of BCLK.
But my chip really can't work at 1900mhz, I've tried all the possibilities ...
The closest I could get was to catch BCLK at 101mhz, and memories at 3733mhz cl14 with infinity fabric at 1866mhz.
With 101mhz bclk the memory actually works at 3770mhz and the infinity fabric at 1885mhz, very close to the dream 1900mhz !!
I got an excellent latency in this configuration, and I am very happy.
Hope this helps!!