Adrian Dodd has been showing how proper tuning can provide real fuel-efficiently and he and his "trained" tuners are getting some decent MPG figures.
How about a similar table on here? Obviously if your Mini is a track beast and not a road car this may all be irrelevant.
I will start with my recently rebuilt 1293 A+. 
Mini Engine Carb Diff Ratio CAM Speed range Avg MPG Classic Mk3
1293
(+20 rebore)
HIF44 3.1 EVO1 50 to 65 48.3
