I enabled the DMA option as you suggested, but I did not notice any change to the severity of the flickering. I also checked ILI9340_SPI_MAXFREQUENCY and it was set to 40000000 just as your example.
I agree regarding the NX graphics + framebuffer usage. No sense in re-inventing the wheel. Now that I have discovered a "hook" into the framebuffer, the NX documentation might make a little more sense. I will revisit and research a bit more.
I will definitely keep this thread updated...I also think it is an important dev topic and worth digging into. Stay tuned!