I do 22 miles each way to work, along M606, M62, M621, usually doing 50/60 mph, standard, the car trip meter (1) read 35-37mpg at the end of the journey, stage 1, with intake, it reads 34-36mpg, so its not a huge difference. This figure is at the end of the journey though, it does take some miles until it gets past 30.
On my 'Road Trip' app, my average of the last 8,000miles, doing motoway driving is 29.7,mpg, so your not far off. My av over 20,723 miles of all driving is only 26.91 with £4,876.02 worth of V-power/tesco99 being burnt