Oh, I got logged in! What a rare surprise!
An interesting question, indeed. Some sources say that von Gersdorff was shot down in a single-seater but I belive he being killed flying together with Speer in a two-seater.
With no doubt they were shut down in Lorraine, not in Alsace(Hanns: did you find "your" Neubourg on the map?).
I always believed the killing place was Nomeny what might be not two far away from Varvinay. But I have no map at moment to check this carefully.