Noted earlier, WD's Blue SN550 is faster during bursty write workloads, but that comes at the loss of sustained performance during longer write transfers. Measuring roughly 7-7.5GB, the SN550's SLC write cache is very small compared to its competitors. After writing at full speed for four seconds, write speed degraded from 1,850 MBps down to an average of just 466 MBps.
The SN550 outperforms both the P1 with its extremely slow QLC write speed, as well as the DRAMless P2 and Silicon Power P34A60. While this sustained performance beats other entry-level NVMe SSDs and your typical SATA SSD, it lags behind high-end NVMe contenders. It did recover very quickly, though. The SLC cache was ready for additional writes at full speed after just 15 to 30 seconds of idle time.