Quick Answer
When upgrading an NVMe SSD, do not ignore matching the PCIe generation to your slot: a Gen4 drive (around R1,200-R1,800 for 1TB, reading 5,000-7,000 MB/s) only hits full speed in a Gen4 M.2 slot, while in a Gen3 slot it runs at about 3,500 MB/s. Confirm your motherboard's M.2 slot generation before buying so you do not pay for speed your board cannot deliver.
Why the slot generation decides real speed
An NVMe drive runs at the lower of its own and the slot's generation. Drop a Gen4 drive into a Gen3 board and it caps at roughly 3,500 MB/s, the Gen3 limit, so the Gen4 premium is wasted. Conversely a Gen3 drive in a Gen4 slot still runs at Gen3 speed. Check your board's manual: many B650 and Z790 boards have one Gen4 (or Gen5) slot plus a Gen3 slot, so install the fast drive in the fast slot. For gaming the felt difference between Gen3 and Gen4 is small, but for large file work it shows.
Heat, lanes and a practical note
Fast Gen4 and Gen5 drives run hot, so use the motherboard's M.2 heatsink, especially under sustained writes, or the drive thermal-throttles. Be aware that a second M.2 slot can share PCIe lanes with a SATA port or the GPU on some boards, dropping a port when populated, so check the manual. Size to 1TB for the OS and games, keep 15 percent free, and only consider Gen5 if you do heavy professional file transfer, since it adds cost and heat for little gaming benefit.
FAQ
Will a Gen4 SSD run at full speed in any motherboard?
Only in a Gen4 M.2 slot. In a Gen3 slot a Gen4 drive caps at about 3,500 MB/s, so the premium is wasted. Check your board's slot generation and install the fast drive in the fast slot.
Do NVMe SSDs need a heatsink?
Fast Gen4 and Gen5 drives do under sustained writes, or they thermal-throttle. Use the motherboard's M.2 heatsink. For light gaming use a Gen3 drive may run fine without one.
Is Gen3 fast enough for gaming?
Yes. Gen3 reads around 3,500 MB/s, which loads games and Windows in seconds, near-identical to Gen4 in felt use. Save the Gen4 or Gen5 premium for heavy file-transfer workloads.
motherboard's M.2 slot generation before buying; put a Gen4 drive in a Gen4 slot with the board's heatsink fitted, and do not pay for Gen4 if your slot is Gen3.