The Mk IX wasnt the only new improved Spitfire at the time, the first single stage Griffon engined Spitfire Mk XII came in in Oct 1942. Wiki says this
However pilots found it difficult to exploit this advantage in combat as German pilots were reluctant to be drawn into dogfights with Spitfires of any type below 20,000 feet (6,100 m). When the Mk XII was able to engage in combat it was a formidable fighter and several Fw 190s and
Bf 109-Gs fell victim to it.
[19] The Mk XII's speed advantage at lower altitudes again became useful near the end of its front line service in Summer 1944, in which it shot down a respectable number of
V-1 Flying Bombs, 82.5
[20] The Mk XII variant was retired in September 1944.