Any engineer will tell you 37.8 mA is 38 mA, and is certain close enough for rock and roll.
I doubt whether you will hear any difference between 38 mA and 42 mA.
Biasing an amp too cold will result in excessive crossover distortion, which I think it is safe to say, is regarded to sound terrible. Certainly my experiences would concur with this view.
However, biasing an amp too cold is perfectly safe.