that's a lotta situps.
I've had to reduce from 600 to 400 because they scrapped my favorite incline board at the gym. The new one is on a steeper angle which makes the sit-ups tougher but probably more effective. I do them in 4 sets.
Wowza! No wonder you're so lean.
I've always been jealous of your sit-up prowess, Tom. Amazing!
Not sure it serves much purpose training wise. May be even potentially bad for my back but so far no problems there.