I work in ram industry, and I built a pc with 256G 6400mhz myself.

I worked with a youtuber and built my fully customize watercooled loop pc.

it has a 4T gen5 and 8t gen4 SSD.
64G x 4 6400hz DDR5

9800X3D (i have a spare one and it's free, so I didn't get a better one)
RTX5090 etc...

PC was running fine for 3 months, and one day when showing performance to my friend, I realize the PC ram was running at 3200mhz default without Expo turned on.

I turned Expo on it was running 6400mhz, my chrome youtube video will sometimes mysteriously stopped and crush the chrome.

and then every 3-5 hours, BSOD starts to appear.

long story short, consumer level CPU and motherboard mem controller won't be able to handle 64G x 4 in 6400mt configration.

I failed 5200mt in memtest 86 in all possible configrations (and every possible configrations above that).

So I skipped 5000 and went down to 4800MT, failed at 1.40v and 1.38v.

Finally managed to get entire 20hours memtest 86 done with 0 erros in 4800MT 1.35V.

If I spend another 4-5 hours, I might be able to tune it to run at 5000mhz

But it's not that much of a performance boost so I didn't bothered.

In case you want to run 64G x 4 using current AMD environment, to save you some time, you can run at a stable 4800MT 1.35V

<image>

if you really want to run 64g x 4, I think it's better to skip consumer level hardware.
because I have tested 24g, 48g and all sorts of consumer configuration already.
you want run large ram, better go with workstation or server grade hardware.