The reality of driving in Germany is that a lot of federal states have maximum speeds on the highway now. And thanks to years of neglect there is a lot of road construction everywhere in the country which means reduced speeds. Speeds are also reduced around cities, around major junctions. And that's usually also where the traffic jams are.
A journey from Berlin to my parents in the Netherlands (525km) would probably take me at least 6 hours normally. That's including stops for lunch, bathroom, fueling, etc. That averages out to about 80-90 km/hour. Only about a fifth or less of the distance allows for driving faster than 130km/h; and usually not for more than 10-20km before you have to slow down for some reason. Driving fast is fun but also stressful because there is always a jerk with a faster car behind you flashing their lights because you are "only" doing 160km/h (100 miles per hour). And high speeds also means accidents are fatal, fairly frequent, and typically result in very long traffic jams.
My experience driving around in different countries in Europe is that you don't get to your destination faster in Germany. Probably France is the most efficient to cover long distances. They have nice, good quality toll roads and you can maintain an average of 120-130 there on long stretches. Spain is pretty decent as well. Roads in Germany are garbage in comparison. There's a reason people are complaining about the state of infrastructure here.
I don't actually own a car and rent cars. Usually, I prefer taking the train, which is not a high speed train even but does that same journey in a bit under four hours. Cheaper, more comfortable, and I can take a nap/relax a bit. Sadly, rail infrastructure is also not in a great state here.