It's the laws of physics. maximum airflow is with no obstructions. Add the grille and it will reduce. Add a mesh and it will reduce. Add badges and it will reduce.
But it's not a linear effect, so standing still it will have no effect. Slow speed will have little effect. At higher speed the engine generates much more heat, so clean flow matters. But without scientific measurements you'll never be able to quantify the effect. Even uprated radiators don't provide a pro rata benefit, because the area behind the grille gets the most flow. You can't extend upwards, and extending downwards is usually masked behind the number plate. The lower you go, the more protection is needed - which reduces flow. A thicker core will help, but because the air heats up as it passes through the core, an extra half inch thickness won't give a proportional benefit due to the preheat. So - just be reasonable, and keep the badges as low as possible - it shouldn't be a problem.
