I have a Denon S920w.
Here's what I just measured. Edit #2: Volume was set to -45.0 on my receiver.
PS4 main menu:
GT Sport Menu Music:
GT Sport Race:
PCars 2 Race:
AC Main Menu (Xbox):
AC Race:
Forza Menu:
Forza Race:
Wildlands is much louder, and it wouldn't make a good comparison to see average db levels. But I think I can measure LFE on this app, I'll have to see how consistent it is. Apparently, according to a NIOSH study, it's relatively decent for measuring sound levels, at least for comparisons against it's own readings.
As you can see, PCars average is well below GTS. I used the AM Vantage GT3 and cockpit view on nurburgring GP for everything except AC, and I used the SLS AMG for that one. I mistakenly thought all the games had the Vantage.
Edit: I have my subwoofer level tuned for movies. It's good on AC, maybe a hair below what I'd like, good on FPS games, great on movies, but low on racing games. Turning it up to be good on my racing games makes it overpowering on movies... and probably at a realistic level on Wildlands. Unfortunately, I can't put a hotkey to change the subwoofer levels with one touch.