I have 30 years experience in the pro audio industry (Engineer, Producer, Musician, Mobile DJ). I have an '04 Tundra LTD dbl cab w/ the JBL system.
Other factors to consider are the types of music you listen to, the tone, balance and fader adjustments and the year that the music was recorded.
Why the last question you may ask? Well, newer music is mixed with higher overall volume levels of sound over most frequencies (pitches) heard by the human ear. The trade-off is that there are less dynamics
(the high volume versus low volumes that were common in recordings from the past). Another fact is that recording technologies are just so much better today than in the past so new recording sound better, fuller and louder.
As far as listening levels: I average between the 20's and 30's in volume when I am alone and want to enjoy my music. When I really want to crank it I will take it to 40 and very seldom beyond
(I, personally, value my hearing).
When I have other people in the vehicle and I am having conversations, it is more likely in the 10 to 20 range. A song from the 1950's may take an extra 10 digits
(of volume knob twisting) to keep up with a newer release. With music recorded in between the 1950's to current day, the amount of "make-up" gain becomes less and less and depends upon the type of music, tonal adjustments, etc.
Keep in mind too that i, personally, rarely have the windows open and prefer the A/C or the vent with the rear electric window down.
Hope this helps!
