Good luck in the competition. I sent you an email, but you didn’t respond. My question is if there is a scheduled event after PBP for CdM?
I agree with sproven, your ftp must be higher. I can see riding at IF=1 for many hours, but not 20. The thing about PBP is there are many big rollers. So riding hard up the hills and resting on the downhills might make for a higher average IF than what is normally possible. Is it possible we can see your ride on Strava?
I always thought that if you had compatriots that could keep up and did the same thing, sleeping at Brest might actually make for a faster time for people riding in the 45 hour range. Do you have a target time? I remember seeing the lead 80hr group returning to Paris in 2011. I was some distance from getting to Loudeac the first time. They looked like I felt, not great.