SPI performance on mono SSH1106 128x64 screen - bulk SPI transfer

For the esp32 case it looks like this flag should be set:

https://esp-idf.readthedocs.io/en/v2.0/api/peripherals/spi_master.html

SPI_USE_TXDATA
It says:
Sometimes, the amount of data is very small making it less than optimal allocating a separate buffer for it. If the data to be transferred is 32 bits or less, it can be stored in the transaction struct itself. For transmitted data, use the tx_data member for this and set the SPI_USE_TXDATA flag on the transmission. For received data, use rx_data and set SPI_USE_RXDATA. In both cases, do not touch the tx_buffer or rx_buffer members, because they use the same memory locations as tx_data and rx_data.