Shouldn't make bit of difference how much you keg with. You don't start out with 12psi and than expect to know how much gets used so you can reduce to 3psi by the time it's almost empty. Also, you size your tubing runs to coincide with the pressure you are kegging with. Would you constantly change the pressure and reduce the length of hose as you drank more and more from the keg?
Primary - Apfelwine
Secondary - Niagara white wine
Kegged - AH Special Holiday Ale, AH Cream Ale, AH Honey Wheat
Bottled - Continental Pilsner, Island Mist Mango Citrus, Island Mist Wildberry Shiraz
Up next - AH Foster's clone, Labatt's clone, Hard Apple Cider,
The Independence Street Brew House