Thanks, corrected.
Ok, "total concurrent", but not without potential bottleneck, especially with the OS divided between disks.
Ok, so as the PCH lanes in B450 are PCIe 2.0 lanes, and PCIe 2.0 running at 2x equals 1.0 GB/s matching the PCIe 3.0 x1 (985MB/s), I should be able to use 4 SATA...