Ha - I've done this! Not quite the same route (I crossed from NED to DE at Venlo) but I did get to Cologne (I carried on through and stopped properly on the way back).
I actually did nijmegen to Bonn in one day - with another 60km on top owing to a misplaced phone. That was real type 3 fun. Great memories though! Basically off the traffic and quality road surfaces for the whole shooting match.
I had no dramas on my 25 mm gatorskins (until one of them split open on the return leg...) but if I were to do it again I'd use 28s. Checking my Strava I averaged 20.2kmh but I hadn't slept the night before owing to a seriously noisy music festival next to my hostel, and had done another 30 km in the morning to go and retreive a phone from a cafe outside of town. Happy days! So you can probably go quicker. You probably won't be carrying as much junk as I did either (party clothes, steel kryptonite lock, etc).
Do yourself a favor and get your food in Lidls. However where you MUST go is Magazin der Ideen 'Lick the Plate', it is the best cake stop I have ever had in my life.
https://www.facebook.com/LickthePlateCakery/aboutI started hallucinating about 40 km outside of Bonn. Started hearing a tennis match in my head and couldn't tell if I was on a hill or not. Most peculiar. I recall getting into my host's flat and just saying 'never, never, never, never again.'
Character building!