I thought this video was rather interesting, because at 12:27, the presenter crunches the numbers to find out how many years it would take for a new computer purchase to be more environmentally friendly (in regards to total CO2 expended) compared to using a less efficient used model.
Depending on the specific use case, it could take as little as 3 years to breakeven in terms of CO2 if both systems were at max power draw forever, and as long as 30 if the systems are mostly at idle.
External 2.5" HDDs connected via USB for longer term bulk storage and using it as a NAS, a smaller internal NVME SSD for the OS and a larger one (but SATA, so slower) for the directory were torrents go to.
The different drive performances fit my usage pattern just fine whilst optimizing price per GB.
External 3.5" would be cheaper for bulk storage but the 2.5" are a leftover from when I was more constrained in terms of physical space.