I have an 06 ST and it gets an average of 26 to 28 combined (90% highway). It has steeda intake and otherwise stock. I have a mildly heavy foot. Usually shift at 2 -25.
Just bought an 03 SVT bone stock. I live in Ohio and i drove it back from texas. I got 30 to 32 while going between 75 and 85 mph using cruise 95 percent of the time. Love the SVT. My ST has never seen over 30 even cruising all highway.