As others my write speeds reduce to around 1200mbs regardless of conditions. I have tried all troubleshoots listed by Corsair.
So been reading another website where a South Korean company who was having same issues has successfully written new firmware that eradicates this issue.
It appears when used as an OS drive that the cache becomes constantly exhausted due to the read/writes of windows.
The algorithms being used to clear the cache are not fast enough leading to degradation in write speeds.
This is a firmware issue and should be resolved by Corsair in update if they are listening!
If the South Korean Company can address it so can corsair!
"South Korean Magic software reported a firmware update for the NVMe drive today. The version number is 3B2QGXA7. The firmware update seems to have fixed all the write cache issues, at least for now."