^^^^I think most people would be surprised just how loud a system can be. Running RTA tests, I had peaks in my car of over 115db by accident.(full range sweeps from 20hz-20khz) The human ear's fidelity of reception greatly decreases above 100db. You will be much more aware of level changes above 100db, than depth and width changes in the soundstage.

My personal experience with source units, is that depth and width of soundstage is the greatest difference between a good deck and a great one.

So for driving down the road with the windows down, a great deck would be a waste. (however I agree about the mood enhancement)

Adam