I get 24 to 25mpg (US) driving about 17miles on a back road, 46miles on a highway, sometimes stop and go. That is total of 63 miles per day to and from work.
The gas mileage is less when the tranny is cold and has to warm up. It takes about 30 minutes to warm-up completely. When the car is used for less than 30 minutes at a time the mileage will be poor.
That is why on, a long trip the gas mileage is good. The SVX is a highway car.
With the windows up and a/c on the air drag is less. So that helps more than the power taken by the a/c.
I too only use Mobil Premium