All of our Goldelox-based display modules have on board protection diodes and 3.3V regulators, they have forward voltage drops. Therefore you 'need' to provide 5 volts to the display modules.
That being said, it is possible to power Goldelox modules down around 4V, sometimes a little lower. By powering the 5V pin as normal there is a diode in series for protection, but by powering the 5V_OUT pin, this is after the diode, so a slightly lower input voltage can be tolerated. Refer to the Schematic in the module Datasheet to see what is actually happening. It will get to a point where the 3.3V regulator will no longer be regulating, and will simply pass the input voltage, however the module may still run correctly. You may have success at 3.3V using the 5V_OUT pin as the input, however you will need to test this yourself. This is not endorsed by 4D Systems, but you are welcome to try at your own risk.