For some reason, recent SSD (solid state disk) product specifications (e.g. from Sandisk)doesn't contain simple technical data as sustained write data rate. As an optimistic interpretation, that's because the parameter doesn't directly count as user performance. I rather doubt, the manufacturers are unable to guarantee a value by design.
In any case, 400 MB/s is far from usual media speed, that is clearly below 100 MB/s and not truely
sustained. So massive parallelization is most likely required, either of 1.8"/2.5" drives or modular devices.