Verdict

For a NAS cache or any write-heavy pool, the MZ-V9P4T0 is the safer pick - the MZ-77Q4T0 uses QLC NAND, which wears out faster and slows down badly under sustained writes. Only consider the MZ-77Q4T0 for light, read-mostly storage.

MZ-77Q4T0 MZ-V9P4T0
Capacity 4 TB 4 TB
Form factor 2.5 M.2
Interface SATA NVMe
NAND type QLC TLC
Endurance (TBW) 1,440 TB 2,400 TB
DWPD - -
DRAM cache Yes Yes
Power-loss protection No No
Sustained write 160 MB/s -
Price / TB $229.23 $156.33

Highlighted cells mark the stronger spec for a NAS build. Failure rates from Backblaze Drive Stats where available; $/TB uses the cheapest live price where available.