Franek, the service ceiling of the PR XIX was 42,600ft (13km). Did they always fly at their service ceiling? Btw, the Spit XIV had the approx. same max speed at the same altitude (~26kft) as the PR XIX and had a service ceiling ~1000ft higher than the PR XIX.
http://www.spitfireperformance.com/spitfire-XIV-ads.jpg