Numerical simulation of DSC traces is used to study the validity and limitations of the Kissinger method for determining the temperature dependence of the crystal-growth rate on continuous heating of glasses from the glass-transition to the melting temperature. A particular interest is to use the wide range of heating rates accessible with ultra-fast DSC to study systems such as the chalcogenide Ge2Sb2Te5 for which fast crystallization is of practical interest in phase-change memory. Kissinger plots are found to show three regimes: (i) at low heating rates the plot is straight; (ii) at medium heating rates the plot is curved as expected from the liquid fragility, and (iii) at the highest heating rates the crystallization rate is thermodynamically limited, and the plot has curvature of the opposite sign. The relative importance of these regimes is identified for different glass-forming systems, considered in terms of the liquid fragility and the reduced glass-transition temperature. The extraction of quantitative information on the fundamental crystallization kinetics from Kissinger plots is discussed.