Maximum SPI speed of TFT display
TSCYCR, Serial clock cycle (Read) is 150 ns. That is 6.6 MHz.
But don't expect miracles of a SPI display. (it might work just fine at 10Mhz)
The software should be optimized to update the least amount of pixels per refresh.

There are still a few things you can do:
- Reduce the color depth.
- Use a longer word. (eg: 16 instead of 8 bit)
- Make sure the SPI routine, if blocking, is as short as possible. Don't wait for the spi to complete, wait for spi to be ready for a new word.

If you want a fast display, get a parallel one with frame buffer you can do operations on.