Wow, I'm amazed at how much performance can be achieved.

The table above shows the relationship between MCLK and UCLK at various DDR speeds. As you can see, once you go above DDR5-6000, the memory controller has to run at MCLK of over 3000 MHz, which is getting close to its maximum frequency limits.

When the 1:2 mode is active, the memory runs at twice the frequency of the memory controller, which means the memory controller can run at lower speeds, which it can handle better. This lets you achieve higher memory speeds without compromising the stability of the memory controller. While memory bandwidth is increased, additional latency is introduced, because the memory controller has to manage the data flow without being able to synchronize perfectly with the memory clock.

Source: https://www.techpowerup.com/review/ddr5-memory-performance-scaling-with-amd-zen-5/2.html

 

Serious Correction: I phoned back to my supplier today, as i'm expecting a couple of Samsung ssds and i spoke with the tech guy again. That particular system turned out to be unstable eventually, after Win 11 install and when gaming. System was tested with COD Black Ops 6 and Baldur's Gate 3. Reportedly my tech friend got bsod in both games. So, he went back to a 1:2 ratio for the UCLK and gaming was smooth as butter.
But what i saw yesterday was outlandish! Remember we were only in BIOS running memtest off a usb stick, that's what i was able to see mainly. It just felt as these 9800X3D cpus are sort of more "cherry picked" silicon than their Ryzen 9 counterparts.
The 1:2 makes sense running smoothly though, as the DDR5 8000 is actually a (double data rate) 4000 mhz ram, so when the UCLK is config'd at 1:2, UCLK and Infinity Fabric Clock (FCLK) run synchronously at 2000mhz. Which theoretically is optimum, as any other speed will have both the unified memory controller and fabric clocks running asynchronously, causing a constant data buffering. Reflecting on this from a serious gamer's perspective though (something which i was really passionate about when younger), this will not have a significant performance increase as timings even with this top end ram are high and will introduce more latency than the most tight clocked DDR5 running at ie. 5600 or 6000 mt/s. This kind of large bandwidth is more suited for productivity workloads rather than gaming.
Still shocked though about the initial witnessing of the 9800X3D build. Well, you can't have it all in one lifetime can you hahaha...
Cheers mate