He has done one Ironman (Kona 2008). In that race he rode a 6:04:55 for 112 miles (the course has 5,814 ft of elevation gain). So he was averaging 18.4 mph
Without knowing his bike setup and how hard he was actually pushing it, it’s tough to get a super accurate estimate. But if we figure he is 6’1" and was say 175 lbs at the time of the race and that he was using at least clip on road bars. I would guestimate his FTP at the time was maybe 250-280 watts. And if I had to venture a guess he was maybe 77-80 kg at the time