Surely Frame Rate depends on how fast you send the 1024 bytes from SRAM buffer to the OLED.
The SSD1306 hardware I2C @ 400kHz means 23ms. i.e. 40 FPS is a practical limit.
Yes, the Arduino Wire library could be improved. e.g. non-blocking
digitalWrite() is not relevant to hardware I2C at all.
Of course Oliver wants to support users who choose to mis-wire their I2C devices.
Providing a bit-banged alternative that uses digitalWrite() means it can run on ANY Arduino target.
Whereas the SSD1306 I2C interface is restricted to 400kHz, the SPI interface is 10MHz.
In theory, you should be able to achieve dramatic Frame Rates.
David.