The official specifications are more conservative than what is possible with memory overclock profiles like Intel XMP and AMD EXPO. The Phoenix tests show 285K at both DDR5-6400 and DDR5-8000. It is possible to go higher than the official 5600 MT/s with Zen 5 as well, but there is less headroom, with 6400 MT/s being the limit according to TPU [1].
[1] https://www.techpowerup.com/review/amd-ryzen-9-9950x/26.html