Don't forget about engine heat...A lot of us remove the rear seats and insulation for weight savings, so as we try and figure out if a system can "keep up" in a particular car/climate, it's important to keep heat intrusion in mind...
This is a relatively stock 1970 911T with a 2.2L engine...It doesn't generate a great deal of heat (or power), but it certainly heats up the cabin. This was after normal around-town driving somewhere around 80°F ambient.
