Disturbance storm time index (DST) is a better measure of peak intensity as KP is just a weighted average of the intensity from the last three hours across monitoring stations.

The May 2024 G5 electrical storm had a peak measured DST of −412 nT: https://en.wikipedia.org/wiki/May_2024_solar_storms

The Carrington Event had an estimated peak DST of −800 nT to −1750 nT, but no one really knows: https://en.wikipedia.org/wiki/Carrington_Event