No they're not but it sure feels slower in AC. In iRacing or rF2 you can definitely tell when you're doing over a hundred miles per hour where as AC you have to watch your speed.Doesn't have much to do with the physics - it's not like the cars are going different speeds than in other sims.
I'd also look into your FOV at first. Note, that some games let you set the FOV in the horizontal pane, in others you adjust the vertical FOV, so numbers might be different.
I have the wind noise ramped up to 10 in the audio menu, while other sounds are on 5, as this seems more realistic to me. I remember that Stefano once said, that they have deliberately reduced the wind sound, as it could be annoying to many. Did you also notice, that there is no tyre sound in AC?
That's true, if you drive Silverstone you feel like standing still compared to a track like Macau. Still, the same tracks with the same FOV in the same sims should give more or less the same sense of speed. With my very low FOV of 26° on my triples I cannot say AC seems particularily slow to me compared to eg rF2 or AMS.One thing I notice is that if you drive a track that has lots of roadside objects close to the road then the sense of speed is better as they rush through your peripheral vision. A lot of tracks tend to be quite open or have grass or distant roadside objects so you don't have so many points of reference for that sense of speed.
What is RHM?Sense of speed in 2D can be enhanced with RHM plugin though it introduces new problems.
I don't know if it can be used with VR and if it makes sense. Worth checking.
To already mentioned roadside objects close to the road I would add track textures that influence sense of speed.