Wikipediaにあったよ。ソースは確認してないけど。

GDDR6X consumes 15% less power per transferred bit than GDDR6, but overall power consumption is higher since GDDR6X is faster than GDDR6. PAM4 consumes less power and pins than differential signalling while still being faster than NRZ.

tps://en.m.wikipedia.org/wiki/GDDR6_SDRAM