What is the expected refreshrate for I2C OLED screens?

[iamisti]

I'm getting the similar effect as the mentioned "SPI screens" slowness on a I2C OLED screen.
I have a small 128x64 OLED screen, but the refresh rate is very very poor. You can even see when the screen refreshes to the newest value.

Also I found a bug with oled.writeString method. Something is not properly implemented, because if I call the method 10-20 times in a second, I get an error:

(node:17852) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 201 I2C-reply-60-0 listeners added to [Firmata]. Use emitter.setMaxListeners() to increase limit

Questions here:

• what is the expected rate of update we can achieve
• why do I get the error (is it a bug?)
• if the update is limited and takes time to execute, wouldn't it be wise to return with a promise, so we can call the next update when the previous screen update finished? There is no way of knowing at the moment when the update has finished

[mind0bender]

I am facing this Error while making a clock.
Is there a way to fix this?