A recent analysis of B 7 K decays concludes that present data do not clearly indicate whether (i) the standard model (or Delta l= 0 new physics) is sufficient. or (ii) Delta l = 1 new physics is needed. We show that these two possibilities can be distinguished by whether a sum rule relating the CP asymmetries of the four B -> pi K decays is valid. If case (i) is favored, the sum rule holds, and one predicts A(Cp)(pi K-0(0)) = -0,15, while in case (ii) fits to new physics involving large values of a color-suppressed tree amplitude entail A(Cp)(pi K-0(0)) = -0.03. The Current experimental average A(Cp)(pi K-0(0)) = -0.01 +/- 0.10 must be measured a factor of at least three times more precisely in order to distinguish between the two cases. (C) 2009 Elsevier B.V. All rights reserved.