I don't know what times you have got using /dev/gpio and /sys/class/gpio, but see attached screenshots from oscilloscope. Software - this exact clock.
Single bit on data line 230ns (freq: 4.35MHz).
Full update of 8x32 pixels + extras 410us (freq: 2.44kHz)
Actually I was a bit surprised, thought it will be much slower.
Now I hope to see more projects from you (and all community)