Thermal Results (Max and AVG) - Write Operations
As expected, the worst scenario is without a heat sink installed on the NVMe SSD and with the cover in place. The max temperature exceeded 71 degrees Celsius in this scenario on the controller. Without a heat sink but with the lid off, the maximum temperature dropped significantly.
The best scenario, in general, is with a heat sink and without the SSD cover. In this scenario, the difference in max temperatures in the controller is close to 15 degrees; in DRAM, it reaches 18.4 degrees and, in Flash memory, it is 11.8 degrees.
Thermal Results (Max and AVG) - Read Operations
Read operations don't stress the SSD as much as writes. Hence the operating temperatures are lower. Moreover, once you install a game on the NVMe SSD, write operations will be minimal, and this is why Sony lists a requirement for read speeds and not for write ones. Similar to the write operations, the removal of the cover brings a notable drop in the operating temperatures of the NVMe drive.
Again the best scenario is with a heat sink and the cover removed, allowing a 9.6 degrees lower max temperature on the controller, 11.9 degrees less on DRAM, and 5.5 degrees lower max temperature on the flash memory.
Transfer Speed Results
Since we already drew our conclusions with the WD drive, there was no need to repeat all thermal tests with the Samsung drive, so we only evaluated the latter on write and read speeds with a 10mm heat sink attached and without the SSD cover, which couldn't close either way.
Data transfer speeds from the PS5's internal storage to the NVMe are notable slower than the WD drive, but the transfer speeds from the NVMe to the PS5's internal storage are around the same. Most likely, PS5's internal drive sets the limitations here. In any case, the WD Black SN850 is faster for PS5 use than the Samsung 980 Pro, although both have the same read and write speeds on paper.
If you don't want to spend on a heat sink and given that the NVMe drive will mostly have to handle read operations, removing the PS5's SSD cover will be enough, as long as you select a fast enough SSD. In our case, the max and average temperatures of the SN850's controller were close to 56 degrees Celsius, with an ambient of 23 degrees Celsius.
The controller in this drive will lose performance and throttle at temperatures close to 88 degrees Celsius, so there is enough headroom. We had about the same operating average temperatures on the controller by simply removing the cover, with the "heat sink installed and cover on" scenario.
The best you can do if you want the lowest possible SSD temperatures is to install a large heat sink without the cover.