oort, there is a big explanation about Gamma Handling in POV-Ray and a short one here Gamma in POV-Ray.
I did some tests and I think that the default (2.5) value assigned to Antialias_Gamma (the one you had mentioned) is the best option and we don't need to play with it. See the contour of the big red ball:
I did some tests and I think that the default (2.5) value assigned to Antialias_Gamma (the one you had mentioned) is the best option and we don't need to play with it. See the contour of the big red ball: