Maybe not much use to the OP, but I have owned both S&B PM2 12-50, and March 10-60 HM. I compared them on the same day, same conditions.
I have sold the PM2 12-50.
March clearly had better contrass and sharpness. Colors were more 'vivid' in day time. I did not compare low light visibility. However, I did compare low light visibility with Kahles K1050, and March was distinctly 'brighter'.
The two other disadvantages of the PM2 12-50 were higher weight, and very short eye relief. I cannot shoot free recoil with 308 FTR loads without being kissed every now and then by the scope.
A fellow shooter had a March 8-80, still has it, but has got two of the March 10-60 HM on his other rifles.
I have also owned Kahles K624i (2nd gen), and own a S&B PM2 5-25 now. The PM2 has far superior glass, sharpness and brightness are superior. Not sure about the gen3 Kahles though. I sold the Kahles K624i.
Will be interesting to compare the PM2 5-25 with the March 10-60 HM. Not apples to apples, but never thought of trying this earlier.