The Chi2-test shows information about the goodness of fit but is less affected by the large number of data points. However, the Chi2 is difficult to interpret (1). First, it depends strongly on the average signal level and therefore a generally acceptable Chi2 cut-off cannot be established. Second, it is not well adapted for time series data, because there is typically a strong correlation between data points in close temporal proximity. However, the Chi2 can be used as a global measure for the residual noise. For a good fitting, the square root of Chi2 is of the same magnitude as the noise in RU.
1. Onell, A. and Andersson, K.; Kinetic determinations of molecular interactions using Biacore - minimum data requirements for efficient experimemtal design. J.Mol.Recognit. (18): 307-317; 2005.