Dornier Do-217P altitude performance
 

Please could people help me trace original sources for performance of the Do-217P?

Among the more bizarre claims are an absolute alititude just over 53,000 feet and an airspeed of 488mph (range 1,300m)

If that's true I think I should just go and trade in my Learjet 35 tomorrow :?)

As a former pilot I know about coffin corner and frankly the Do-217P would need a fairly high speed just to avoid stalling at such altitudes, but who originally generated this claim of 488mph?

Does anybody know the intended mission requiring such altitude performance and why was it considered a bomber by the Luftwaffe?