Albertporter...I don't want to get mixed up with the power cord thing, but perhaps you could explain why you think (pronounce actually) that, in general, a long term listening comparison is better than a quick A or B. In my experience long term comparisons become very subjective, so that it is easy to "hear" differences that don't really exist.
I agree that long term listening is the best way to determine if you really like the sound, but, to detect changes, I think that the quick A or B is best.
I think people are under too much pressure to make a decision when confronted with A or B. Why should a change in your audio system be based on a decision made in 10 seconds or less?
Have you not ever made a decision too quickly and later regretted it?
If you are truly able to tell what makes you happy in that quick a comparison, I wish I had hung out with you in college. You could have helped keep me out of decisions I made, particularly with women.