6400MHz isn't minimum guaranteed RAM speed that is the
MAXIMUM guaranteed RAM speed. Even Intel's Ark says Maximum Memory Speed: 6400MHz.
https://www.intel.com/content/www/u...-36m-cache-up-to-5-70-ghz/specifications.html
While Tom's Hardware was able to test with 7200MHz UDIMMs that doesn't mean that everyone will get that speed. Odds say that the Ultra 9's have the best
chance of hitting RAM speeds beyond 6400MHz but again that isn't guarantee. I've seen people complain that they couldn't get 6000MHz RAM to work on an Ryzen 7600 at rated speeds but would work at 5600MHz. Well they didn't win the silicon lottery so their RAM controller couldn't go to 6000MHz. This is why even for Ryzen 9000 series the maximum guaranteed speeds is only 5600MHz. Therefore AMD testing at 6400MHz isn't using "slow RAM" despite what you think.