I use 40. Any threat under that is usually MRCD which isn’t affected by the muting on my R7 and it still gives me a short audio warning before muting other signals too. Generally I find roads that are a lower PSL than 40 I am not moving much more swiftly than the PSL anyway just due to lights and traffic etc.
I keep mine at 30 but I have thought about lowering it to 25. Seems like, maybe not, auto lockouts do not apply to signals that are muted via low speed muting. If thats right, something about the speed I could go in a parking lot or garage is where I want the setting to be. That way, auto lockout can apply to everything else.