A short update. I switched out the 400s in favor of the 25s, as suggested. Currently my week looks like this:

Mon: 30x50 USRPT
Tue: 20x50 chords
Wed: 1600y recovery swim
Thu: 30x100 USRPT
Fri: 1600y recovery swim
Sat: 30x25 USRPT
Sun: 15x50 chords

Current USRPT set Paces (first failure/total completed at pace):
USRPT.25: 18.2 (#14/24) 1:13pace
USRPT.50: 42.5 (#21/30) 1:25pace
USRPT.100: 1:34 (#12/21) 1:34pace


I'm guessing that the USRPT.50 set would really be at 1:23pace for a failure in the 12-14 range (similar to the 25s and 100s). That would put my fall off over distance at 12% per doubling between 25/50/100.

I missed 6 days around Christmas, it took me a about 5 days to get back to pace, and begin to see improvements over paces/reps before the break. Last week was largely re-plowing the ground I'd plowed before the break. This week was the first uptick over my last swims of 2018.