The 135 vs 150 question comes up frequently. This chart shows the "S" versions of theses lenses. Green is the 135 and red is the 150. Three apertures and three maginfications (solid = high, wide dash = medium and short dash = low). Details on the Schneider site.

Comment: Yes the 135 has more light falloff across the board than the 150, but the magnitude is small compared to the changes in magnification and aperture presented in the graph.