The 4-cyl,manual 5-speed,2WD,T-100 was good for around 26.4-mpg,naked,at a steady 65-mph,on Regular Unleaded.
With the aero kit I've seen 39.9 mpg three times.
With a modern GDI engine you could multiply that by 1.15.
With a modern turbo-diesel you could multiply that by 1.3.
'Hope to break 40 next year.