External ram may be part of the equation too, but it really depends on the ability to page the buffer to the display. i.e. putting it on the same serial bus and switching the chip selects so when it reads out, it sends it to the screen directly from the ram.
Color, honestly, if we want to keep it the size of a credit card, won’t happen. It doesn’t fit and the power consumption is too high for our small battery.
Id love to get gray scale with the custom oled but we probably need to order a million units to get that… Still plugging away trying to get in with the manufacturer.
So it seems the arm-0 with SD card and potentially some ram could be a nice option, same screen.