I tried this yesterday and found it interesting. The pool was rather busy so some of the results may be affected by drafting off faster swimmers, being impeded by slower swimmers (admittedly these are less common than the faster swimmers) and so on.
I started at 1:60 as you suggested and my first length was 19 strokes
At 1:65 I think I did 18 strokes, and then a couple of 17s.
I managed one length in 16 strokes but I don't remember which one. It is very unusual for me to do less than 17 so that convinced me to try this again. Maybe starting at a slightly faster tempo and going up (and down) in smaller increments - say 1:40, 1:45 etc...
When I finished the set I thought I would start over again but the mojo seemed to have deserted me. Nevertheless it was a very interesting experience.