I have a couple of older OLED 160x120 displays, one of which shows firmware 2.7 on boot. The one that shows that firmware version also takes much longer to boot than the other one. The slow one flashes solid screens of various colors before showing the splash screen. That takes ~4 sec. before a command will have effect. The other one seems much faster, accepting commands after just a few hundred milliseconds. I'd really like to reduce the boot time and make them both consistent. They are both on I2C mode. 

Do I understand correctly that I cannot update the firmware on these displays? If I order new displays will they come with the current firmware, which can be upgraded?

Thanks. 

Only 3.5B and later version suffixed with "B" can be upgrade able.

Your problem is not about the firmware version, the faster module you have was disabled to show the config, you can use command "DC0" to make the slower one to be faster when power up.