Before you go off half-cocked...a proper heat load calculation must be performed on YOUR place. Depending on the construction, insulation, window sizes, orientation, and placement, there is no valid one-size per square feet calculation that will do you justice. If the calculation determines the ideal size is inbetween available sizes, you always want to go to the lower sized unit, not the larger one. An a/c unit works best if it is running all the time. A big one will make the space cold but clammy, since it only runs a short time and can't dehumidify. Now, I suppose in the desert that has some merit, but not for longevity since things work better when they aren't turning on and off all the time.