Finally added some variety to my workout. After warmup, I alternated 25 drill/swim and did a "shark fin" drill that I learned from watching my kids on their new swim teams. The workout core was 6 x 100s (10s rest). I did these between 1:35 & 1:40 (not terrible). Then 6 x 50s (on 1:00, odd easy, even hard). I went as fast as I could without compromising my technique. Stroke ok but the workout felt great.