Is a Samsung 990 Pro 1TB worth upgrading from a Lexar NM620 512GB?

The 990 Pro is a higher-end drive with DRAM and much faster sequential speeds, but those advantages mostly show up in benchmarks or heavy file transfers. For game storage, even a decent SATA SSD is often close enough because games are largely reading data after installation. Buy based on price per gigabyte unless you regularly move very large files.

The capacity increase is the main benefit. Since the NM620 is already an NVMe SSD, switching to a much faster PCIe 4.0 drive probably will not noticeably improve gaming performance. Games mainly benefit from faster load times, not higher frame rates, and most titles do not fully use the difference between these drives. A cheaper 1TB SSD would likely provide almost the same gaming experience.

Moving the operating system to the 990 Pro could improve some disk-heavy tasks and might reduce boot times slightly, but everyday use usually will not feel dramatically different from a healthy NVMe drive. RAM, CPU performance, startup programs, and the operating system itself often matter more.

For games such as GTA V, an SSD can help compared with a hard drive, but replacing one NVMe drive with another may only reduce loading times a little, if at all. Long waits can also come from the game engine, CPU, system configuration, or online connection, so a 990 Pro is not guaranteed to fix them.