This program calculates the FPS of a i2c 128 x 64 OLED. It could ,however, be adapted to use with other OLEDs.
On a Pi Zero I got 3.7 frames per seconds but this can be improved my following this (https://www.raspberrypi-spy.co.uk/2018/02/change-raspberry-pi-i2c-bus-speed/) tutorial.
On a Pi 2B I got 6.1 frames per second and this could also be improved by looking at the tutorial linked above.