It seems that just like in freestyle there is diminishing returns in making your stroke super long and it instead becomes a hypoxic underwater swim similar to combat swimmer stroke (which is great fun to play with by the way). CSS probably has the lowest stroke rate.
Long stroke combat swim stroke: https://www.youtube.com/watch?v=ctpfSa-gthk
CSS with breaststroke kick: https://www.youtube.com/watch?v=zeS0W--PGIw
(swimmer has some fidgety nervous unnecessary flutter kicks in there that shouldn't be)