Out of curiosity, I had a play with this board,
https://www.waveshare.com/wiki/Pico-Eval-Board
Unfortunately there is a hard speed limit of about 1.5M pixels/sec using 16 bit colors (due to the SPI to parallel conversion circuitry hardware, which maxes out at about 24Mb/s).
I am currently running the RP2040 at 267MHz and intend on tweaking the code to use the second core to do flushing, but I doubt it will result in any really meaningful performance improvement.
This is not a great performer speed wise but at the price, (around $30 all in, excluding the pico itself which should cost less than $5-00) a 3.5" 480x320 display with touch capability it is never the less usable and useful for some applications that are not performance critical.
