Dell t5810 - will populating all the 8 ram slots with memory dimms lower the memory speed ?

Hello people ! I have this question for the people that have populated all the ram slots of the dell T5810 and can give me a real 

world experience. I would like to know if for example the speed decreases with 128gb or 256gb max with all dimm's full.  I am 

asking all of this because the manual says " NOTE : If all DIMMs are 2133, the CPU ordered may run the memory at a slower speed. "

I am interested  what happens when the memory sticks are 2133 paired with a v3 cpu ( this is what was available probably when the 

manual has been written) but i am interested especially what happens with the memory speed when all slots are populated with ddr4 

2400 paired with a higher core v4, 12-14 core .

I have added a screen capture and there is the link where it's written in the 

manual that the memory/cpu will have lower speed :

https://www.dell.com/support/manuals/en-ro/precision-t5810-

workstation/precision_t5810_om_pub/memory-module-guidelines?guid=guid-95c34f6c-d733-4611-952b-4b512b619262&lang=en-us

In real world 

after so many bios updates and support for the v4 generation of broadwells is it really like that ?