...this will certainly make a real difference in days and days and days less traveling on such a long trip...Could mean a cross country trip time could be easily a week or two less than on a bike with 40lbs of stuff, plus you save on accommodation, food costs....
Exactly my experience, though much more pronounced than your "guesstimate". On a recent 4500 mile transcontinental tour with my newly-lightened rig, I budgeted up to 80 days and US$3,000 based on previous trips. The trip took 55 days and only $1,500. I had never ridden a century before with a fully-loaded touring bike--I did 17 on that trip, with three in a row once. I was tempted to turn around and go back.