Not really. I usually set the cruise to 85mph (according to the sat nav, not the speedo), and sit there watching for numpties & BiB on bridges, for 200+ miles at a time.
Most of my miles are like that, and only 50 or so at the weekend are around town. So the average MPH is quite good normally.
Just before this last reset, I'd done a Liverpool to Birmingham, Birmingham to Swindon, Swindon to Birmingham, Birmingham to Swindon, Swindon to Basingstoke and Basingstoke to Colchester over the course of 3 days and covered 600 miles at an MPG of 24.8 and average MPH of...error...signal lost...