Did a 70 mile journey today with mainly dual carrigeway (2 up, winter tyres 40PSI, half tank of vPower, outdoor temp 9*C, little wind, heating on 19*C, xenons on) with some town... overall... 41.1 MPG!!
Stage 1 with Pre-Cat delete... was effin' boring though, lol. The odd flutter to 85mph to overtake but mostly 65mph and a few 50 zones just coasting.
Mad what you can get out of these when your being very sensible, anticipating the traffic, brushing the throttle! Try above with an ST and you'd be very lucky to get 30-33MPG
Based on 41.1MPG and a 12.1 gallon tank that would be just under 500 miles to a tank....but I honestly don't think I could last a whole tank driving like that... very relaxing though! And it's not like your holding anything up.