Here are the videos of the speed improvement from 16 to 25Mhz SPI speed:

@ 16Mhz

@25Mhz

It's not very noticeable as the speeds start to match the phone's camera fps. So we'll look at the counters instead.

It counts to ~102M on 16Mhz and to ~72M on the 25Mhz for a set o 10 frames (16 bit mode). There's a bug somewhere because I clear the timer value from one iteration to the other but it keeps the value. So I added an extra line with the difference on the bottom.

This results in a time reduction from 126ms to 90ms for a single full frame write. Equivalent to about 11fps. Not super smooth but I won't be running video on this :)

More than enough considering the SPI interface and the "big" screen resolution.

I could improve even more by using the SPI FIFO but doesn't seem to get a lot more than this and would require a lot of SW changes.