Column 6 is your response variable and columns 1-5 are your factors.
You are asking for the sensitivity of the response to the factors. It can be determined by calculus and new variables can be calculated in new columns. Then, the column that has the maximum value is the one that has the most effect. The sensitivity is a function of the actual values, so it could be different at each point in the domain of the factors.
Sensitivity is determined by looking at the equation itself. The equation is:
Y = Flow * (A-C) / (B-D)
By calculus we get these sensitivity equations and you can create them as five new columns each having a formula.
SA = dY / dA = Flow / (B-D), units are flow per degree
SB = dY / dB = -Flow * (A-C) / (B-D)^2, units are flow per degree
SC = dY / dC = -Flow / (B-D), units are flow per degree
SD = dY / dD = Flow * (A-C) / (B-D)^2, units are flow per degree
SFlow = dY / dFlow = (A-C)/(B-D), units are dimensionless