mpg on my 340

Very satisfied with my mpg for hwy driving, was worried because of the poor 10 mpg I was getting in town driving. I have a 68 cuda with a 340 and 750 quick fuel carb, jetting at 66 with a power valve on the primary, 72 jetting in the rear. Idle circuit adjusted to 3/4 turn out on both. Made a test run this week and took off down a river road with no red lights, I got 16 mpg, would like to hear a few similar mpg avgs for similar set ups.3.23 gears and 904 3 speed automatic, headers and dual exhaust.