Apple M3 uses LPDDR5 and have transfer speeds of up to 6400 MT/s while LPDDR5X will have 8533 MT/s.
LPCAMM2 is the connector type to replace SO-DIMM slots, it still uses LPDDR chips. According to this article, it would support speeds of up to 9600 MT/s. So unless I'm missing something, shouldn't speed not be much of a concern? I'm open to corrections.