The safest way is to set driver to the highest torque you can handle, but with that you essentially derate your wheel making it run at lower amperage.
It could be critical for sims like iRacing that have no control over signal strength when collisions occur, with AC/ACC, it's pretty safe to have driver at 100% and just lower gain in game.
As far as the actual final result goes, outside of clipping that can occur with too high in game gain, there shouldn't be any difference.
My personal preference, if game has gain setting, use that and just leave driver at 100%, I am sure plenty of people disagree with this approach, iRacers in particular.