The airspeed referenced was taken from a German document provide by a knowledgeable source of Fw aircraft and is possibly a copy of an Fw document. It does not call out aircraft number so it may be an engineering estimate. It certainly reflects GM1 used at 11.5 km alt. and probably does include MW50, although I don't read German. It provides no data on climb.
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Would you please make the doc available for download (if it's in an electronic form), or point to it?