50.6.4.1.2 Host Read Mode

f SPCK max = 1 SPI 0 or  SPI 3 + t valid

tvalid is the client time response to output data after detecting an SPCK edge.

For a nonvolatile memory with tVALID (or tv) = 5 ns, using SPI3, fSPCKmax = 50 MHz.