Indeed, a 4% difference compounds quite well. Unfortunately many people imagine they might get a 3% or 4% net bump, when they are really going to get 1% extra.
Working an extra 20% so that you are paid appropriately larger salary 19 years down the line is not a terrible choice if you really need the money. It is also possible you will earn true grade improvement along the way and get a one time additional bump of 5% for your effort.
Of course, if we reverse the equation, things might look differently. I have about 3 potential free hour per workday and 12 free hours per weekend day, for a net 39 hours of "my own time", earned by showing up to work. Giving 10 hours of those to the employer is a "pay cut" of 25%.