With a split-level house, I need to adjust the thermostat kinda often. It's main floor, and half-level up and half-level down from there. It seems to be at least a 4° difference each level, so a normal 72° main level means hot upstairs and cool downstairs -- so it depends where I'm spending my time.
Consider putting in a two zone system. It may cost you $3,000 or more but in the long run it's a lot more convenient and you'll save some bucks eventually.
