How does this play in with the fact that the DDR5 is clocked at 4800mHz and the DDR4 is at 3200? Would we not expect a 50% improvement with respect to transfer rates with a 50% increase in clock? I really don't know.

There are even 4800mHz DDR4 DIMMs available now, even if they are niche.

EDIT: DDR4 is 3200 not 3800.