Suggestion noted, Werner. But I'm a very poor pupil, so I won't do that :)
Rather, as with the 100m repeats, I'll stick at 200m until it becomes trivial, and then double the distance again.
I would like to do something about my stroke rate. I know it's too slow. But for now, it's not the priority. Next year I will start using a TT. And then I'll have to wear a swim cap too, and look like a proper swimmer!