Both are operating at a low speed 250KHz. On the Slave I can print the SPI Control Register (SPCR) to verify the settings but on the Master:
// Why doesn't this work on ESP8266?
Serial.print("SPCR(bin) = "); Serial.println(SPCR, BIN); // View the SPI Control Register (SPCR)
It tells me "SPCR not defined in this scope". WAT?