I've modified the SSD1306 code and got it working with an SPI interface. Most of the initialisation code is the datasheet defaults. I haven't tried I2C, and can only test 64 pixel display height, but all that code is still in. I've added an option to rotate the display so that the pin header can be at the bottom, however there is almost certainly a better way of doing it.
I've yet to write SH1106.md, and then wrestle with Github, which I've not used seriously before.
Edit: I've got round to actually reading the Graphics class documentation, and my rotate code is redundant, so it's coming out.