The three families
2.5" SATA III SSDs cap at ~550 MB/s sequential read - the limit of the SATA bus, not the flash. M.2 SATA III SSDs hit the same wall in a smaller form factor. NVMe over PCIe is where speeds open up: Gen 3 x4 reaches ~3,000-3,500 MB/s, Gen 4 x4 reaches ~5,000-7,000 MB/s.
When SATA is fine
Boot drive for a general-purpose desktop, secondary storage for a laptop, anywhere the workload is dominated by small random reads. The user-perceived difference between a SATA SSD and an NVMe Gen 3 drive in a typical office workflow is small - both feel instant.
When NVMe Gen 3 is the sweet spot
Modern laptops and small-form-factor builds where you want speed but the platform doesn't expose Gen 4 lanes. Also a good fit for sustained workstation workloads - editing 4K video, working with multi-GB project files, running VMs - where Gen 4 won't show a meaningful real-world advantage.
When NVMe Gen 4 actually pays off
Sustained sequential workloads at scale: large-file ingest pipelines, scientific data captures, AI training datasets, hot-tier storage in workstations or servers. If your workload moves multi-GB blocks at full bus rate, Gen 4 is the right choice. Otherwise the headroom sits idle.
A practical decision rule
Match the drive to the workload, not the spec sheet. Most home and office users will get more durable benefit from doubling capacity in the same family than from jumping a generation in the same capacity.