Assuming the errors are random and uncorrelated, the total significance is the square root of the sum of the squares. In this case, that's only 4.3 sigma.
I generally treat particle physics as a black box from which magic appears, but my understanding was that 3 is where things start getting interesting, and 5 is where it's considered pretty conclusive, so wouldn't going from 3.5 to 4.3 be a significant jump?
