What jsilva said, and I would add …
I use 2x WD40EFRX-68WT0N0 and 2x WD40EFRX-68N32N0
Under light load the two WD40EFRX-68WT0N0 run at 43° C and the two newer run at 40° C.
Also it is noticeable that the older model is noisier and vibrates more than the newer model.
Both models are relatively silent compared to WD Blue or others, but you can tell the difference between the two reds above.
A single one shown 3-5 unreadable bad sectors while still working fine and without funny noises.
It was the newer model but also the one used the most at that time.
