Write speed with MX25R6435F on nrf52840dk

Hi everyone, I am testing out the qspi flash on pca10056. While the read speed is decent around 650 KBs, the write speed is too slow ~ 35 KBs. It could be our own usb/caching software. But I wonder if anyone here got any better write speed in general.

Noted: I have enabled  QUAD mode with writeoc = NRF_QSPI_WRITEOC_PP4IO, with speed = 32 Mhz div 1, and High performance bit on  MX25R6435F