I read on other website that apparently there are versions not following original design and not having regulator at all, which means 3.3V is required. See
The information you quoted come from
here and is only related to the Bluetooth module. OPlink will not work correctly using 3.3V.
Recommended voltage is +5V to 2S Lipo battery (8.4V), the 20V max limit do not take in account the needed power dissipated.
Best option is connect the Oplink to the +6V or add a small +5V regulator connected to the +Bat