If you can't, there's seriously something wrong with you.
On my "grocery getter", I went from 1.95 to 1.75 to 1.5 to 1.25"
There was a noticeable improvement every change, else I wouldn't have kept changing.
Yea, i can always tell the difference, especially if tires are same pressure for comparison. That said... I used to ride 80/65 front/rear because that was the max spec for the tires, and you could feel a huge difference if the front tire dropped below high 60 psi or the rear below 60 due to the weight distribution. So, i guess the key either way to get that better miles per effort is to have whatever you're riding on properly inflated!!
I can't wait for the next pint of good chocolate milk after a long ride.