Let's assume there are two approaches to determining the tempo of this fugue. One is to play it slowly and solemnly, as on a pipe organ, at approximately quarter note = 58. If proceeding at this tempo, it would be more natural to connect the six consecutive eighth notes in the theme with legato or tenuto.

The other approach is to proceed at approximately quarter note = 110. If proceeding at this tempo, it would be more natural to use staccato for the six consecutive eighth notes in the theme.

While neither approach is incorrect, considering that the theme is quite long, spanning five measures, and that its entrance, like the tenor's theme in measure 20, begins on the second beat and can easily be obscured by other voices (making it difficult to highlight the theme), it becomes clear that playing this fugue at a faster tempo makes it significantly clearer, easier to play, and easier to listen to.

The progression of the double (in thirds) voice starting from measure 59 also tends to become heavy if the tempo is slow.

Ultimately, the performer must decide, but the author would recommend the faster tempo.