Most of our testing with the SSD990 EVO PRO was done at Gen4 x4 but we did install it in our Gen 5 test rig to run a few tests to see what the Gen5 x2 option brings in terms of performance.
The biggest difference we saw came from using the random QD32 T16 test in the Peak Performance profile in CrystalDiskMark 8. With the Gen 4 interface, we couldn't get close to the official maximums of 1,000,000 IOPS and 1,350,000 IOPS for reads and writes, respectively with test scores of 778,923 IOPS for reads and 577,895 IOPS for writes. With the Gen 5 x2 interface, we could confirm the official read rating with a test result of 1,021,378 IOPS, but we were still short when it came to the write performance, at 1,271,162 IOPS.