Currently your best option for running 64GB DDR5 is getting a 2x32GB kit.
Provantage had the Crucial 2x32GB kits up for sale back in November and I ordered one kit,.. a week later they sent an email notifying my order was sent to Crucial Direct Warehouse and my kit will be shipped direct from Crucial,.. after waiting 4-weeks I canceled the order yesterday.
Hopefully more venders will release 2x32GB kits soon, but for now only Corsair, and Crucial have actually released kits.
Corsair 2x32GB DDR5 4400MHz CL36. https://www.corsair.com/us/en/Categories/Products/Memory/VENGEANCE-DDR5-Memory---Black/p/CMK64GX5M2A...
Crucial 64GB Kit 2x32GB DDR5-4800 CL40. https://www.crucial.com/memory/ddr5/ct2k32g48c40u5
Like the topic says, can't get 5200 to post for 64gb/4 sticks. If I run 32 gigs at 5200 it works no problem, xmp or manual no problem. I managed to get ahold of another set and it won't post at 5200 manual or xmp. Seems very finicky. Looks like 64 gbs xmp or manual are too much for the memory controller on the z690 extreme board. Any1 manage to get 64gigs running at 5200?
I have Z690f gaming MOBO with i9 12k9
4 sticks x 16 XPG DDR5 , update your bios to the newest bios version (2305) - update your IntelME too ( as recommend from asus)
After that, set your A.I Tweaker in bios setup into XMP1, and set DDR5 bus = 5200 MHZ
Save your settings and enjoy !!!