it reads about 12-12.5 when it's rompin' time and I have these wonderful eyebrows of black soot on my rear bumper (idk if I would get that with a stock tune without CATs also) but I drive about 90hwy/10city and normally get about 19-21 also greatly depending on how often I use the A/C.
"The dreaded 2nd windshiled wiper swipe when you turn it off its almost like tis showing you that it's boss, and it doesn't have to stop when you tell it to :("-College Boy