[_archon_]

You may find some cheap, easy gains by adding thermostatically controlled fans to your attic's soffet vents. It can get very hot in an attic on hot, sunny days, even if the floors below are held in comfort by A/C. Forcing the (hot but not nearly as hot as attic air) fresh outside air in (especially during the cool night, then idling during the day) can reduce the work your A/C has to do.