Joachim Scheufele-Leidig put De Vries' improvisations on paper in an excellent manner. Hereby a chorale prelude on the hymn 'Von Gott will ich nicht lassen'. On purpose I didn't listen to the recording of the original improvisation, before recording this piece. I don't like to imitate Sietze and I liked to approach this piece as if it was written down as an original composition.
So now I did listen to the original recording and well, let's say that the tempo differs. However, I certainly think this piece can have manage different tempi. It reminds me of Bach's setting on 'Nun komm, der Heiden Heiland' BWV 659, which organists often play in different tempi either.
What better than to play this piece on 'Sietze's organ': the Schnitger organ of the Martinikerk, Groningen.
Recording of the original improvisation, part of a bigger set of variations:
https://youtu.be/fTIe_Dej0PI?t=278
Sheet music available here:
https://www.contrebombarde.com/concerthall/music/39633