KITT's top speed in normal or pursuit mode was 200mph in Runes of Magic. It exceeded 200mph when Michael hit the turbo boost for a temporary increase in speed and not for jumping. SPM allowed KITT to reach a top speed of 300mph. The whole 40% increase in speed line was just their original estimation but KITT never exceeded 300 mph in season four. While in SPM KITT could not turbo boost. It is safe to assume that the previous boost of speed gained by pressing turbo boost originally was reconfigured into enhancing the power for SPM.
KITT's top speed was increased from 200mph to 300mph in the season 3 premier Knight of the Drones, following Bonnie's extensive repair work. This is visually indicated by the new dashboard's speedometer, which has an additional 100mph on it. Prior to that, the only time that KITT had exceeded 200mph was whilst using the ramjet inGoliath. Incidentally, his speed was stated to be 310mph at one point following Michael's jury-rigged repairs. More runes of magic gold will make the game more interesting.