I've driven a few laps of it in ACC. First of all, as far as I can tell, you can only drive the 24 hour track, not Nordschleife without the Nurburgring GP section. Apart from that, it felt very similar to the track in FM to me. There might be some small differences in the shape of everything in places, e.g. one corner where I struggle to not run wide on exit onto the kerb in FM, I found myself exiting noticeably short of the kerb in ACC, so maybe that edge of the track isn't quite in the same place in the two games. But if you just pick one of the games and only play that game, and get used to its version of the track, the experience is going to be largely the same. I haven't compared the night versions as I don't like driving at night, so it doesn't really matter to me.
I did notice that the braking in ACC felt a bit off. The car didn't seem to scrub speed off fast enough at lower speeds. I did a few maximal braking tests on a straight while looking at the speed, and I'm not sure what is happening is correct, but I haven't spent the time yet looking up data on the downforce vs speed relationship in GT3 cars to create my own simulation of how the relationship between speed and rate of speed reduction should look, not sure if I care enough to do it. At the moment, FM feels like a better driving experience to me, but FM is the driving game I've played the most recently, and I think there is an element of everything else feeling worse than the game you're most used to.
