It was amazing to watch them and this clip just brought back the images. As far as how fast they were going, I heard DrD was bouncing off the rev limiter in 4th gear on the downhill between the big step up and the smaller one. Watching both Coop and DrD wheelie up that uphill after the smaller step up definitely showed their speed and technique.
The other thing that was amazing was Coop wheelie-ing the off-camber after the finish jump! That thing was slippery enough on 2 wheels -- can't imagine doing it that fast with the front end in the air!