This is a great and very important question because in many compositions of the Baroque period composers didn't leave any precise tempo indications. When you don't have a tempo suggestion written in (like Adagio, Moderato, Allegro etc.) nor metronome markings, how are you supposed to figure out the concert tempo at which to perform in public?
In order to answer this question about many pieces from the Baroque period (like this chorale prelude), we have to take into consideration these 7 things: meter, acoustics, mechanics of the organ, your technique, hearing, singing style, and breathing.
1. Meter of the piece. Generally speaking (but not always), the smaller the beat value in the composition, the faster the tempo should be. For example, 3/8 is faster than 3/4. Count the beats and pay attention to the alternation of the strong and weak beats. This will be helpful in slow pieces.
2. Acoustics of the room. The space that you are playing in will be one of the major factors in determining the speed of this piece. If you play in your practice room or at home, you can perform much faster than in a cathedral or church with huge reverberation.
3. Mechanics of the organ. The type of organ action also determines the tempo of this piece. In general, if you are performing on the tracker or mechanical action instrument, try to play a bit slower because of the action. On the other hand, if you are playing on the electro-pneumatic or electronic organ you can play much faster.
4. Your technique. If your technique is not developed enough, naturally you will not be able to play very fast. In this case, choose a tempo on the slower side of the spectrum which you would be comfortable with.
5. Your hearing. Try to listen attentively to each harmonic turn and dissonance. This is particularly challenging to organists who have great technique and want to show off their virtuosity. Remember that in the Baroque music, we are showing off the music and the musical story and not ourselves.
6. Singing style. Try to retain the cantabile style in the performance of the piece. Even the fast pieces should have this character.
7. Your breathing. Try to sing with full voice the phrases with one breath. This will help you choose the tempo which would not be too slow for the musical flow.
Keep in mind the above 7 tips when you try to decide what kind of concert tempo is best suitable for you and your piece. Since we all are different and play in different spaces with different organs, the tempo may fluctuate quite a bit.