52.1 kph by Mads Pedersen on a distance of 41 k. That's not bad, is it?
163 hm on 40.9k / 0.4% avg climb I personally regard as "severely flattish" compared to my usual 0.9-1.3% avg training routes. Which advocates for high average speeds.
However, almost all altitude was gained within first 5k or so, out of Nr. Sundby, moreover Vendsyssel is usually quite windy and generally different weather compared to south of Limfjorden.
I was not in my old proper as of yesterday, even not been able to watch the races yet so don't know exact conditions in the north.
On a windless day in the area, without taking into account the hills at Lindholm Høje, you can really get up to speed, suitable for the airport. Here I wouldn't say avg 52.1kph @ 40.9k for pro TT riders isn't something to write home about nowadays...
But if yesterday's TT Championship has been with a mixture of the stiff northwest wind and the challenging gusts, then it is definitely a high speed.
I read a bit of Nicklas Larsen's post race interview that he didn't "feel he had enough speed" (but still #2 just 25 secs behind Mads).
To me it sounds like the mischievous constant northwest wind, which you may not notice and feels like a false flat - in that case 52.1kph avg. is surely impressive!