Driving fast is fun for about an hour or two,
at which point... you're there!
I was comfortable doing about 170-180 km/h, at which point I think I found a good balance between slow and fast vehicles.
We traveled on a Tuesday. I found that 180km/h was still an inadequate speed to maintain in the left lane. Plus, it seemed that any time I could let loose, there was another interchange looming ahead with another speed reduction. I tended to maintain 150 in the center lane and then latch on to a line of speed demons after they passed on the left.
I should also mention the difficulty with reading guide and warning signs at these speeds, especially when some of the text is ~6" high and often there is foliage that comes right up to the guardrail, obscuring the sign's message until you're almost on top of the sign.
The interesting thing was being passed by the ICE train when we paralleled the tracks for a short time.