You forgot about temperature dependence differences.
I hope the temperature is about the same.
The BME280 has to be set into the highest and slowest accuracy, and that number can be averaged even more in software.
How fast should they respond ? Is the average during one minute okay ?
I don't know what you want with the highest rating.
When they are side by side, you could take the average during a minute and store the offset for one (or both) in EEPROM.