I have done this multiple times. Another set I’ve done multiple times is 10x200 on 2:45 coming in at 2:39-2:42. If I’m tired the last two might be touch and go, but i don’t think I’ve missed.

About two weeks before the high 31:50 I did a set 4x400, 4x200, 4x100 no breaks on 1:30 and I swam under 1:20 pace for everything except the first 400, which was 5:22. I felt controlled the whole time.

I must be weird because i find the lactic acid buildup in my shoulders is way less in a 25m pool versus 50m pool. I felt like i couldn't swim when i switched from indoor 25 in Winter back to 50m in Spring, after 75m my shoulders would die. Where in the 25m pool i could push to the point of near spewing with a high heart rate as my muscles didn't seem to be the limiter.