Hi Tom, 33-45. Really drops off above 60 mph. Winter fuel, riding below 3,000 ft, rider position, use of high drag lubes, low state of tune, old O2 sensor and plugs all cut economy. 1100's are better on fuel, 50 mpg common.
Tell us more about the prospect 1150. "Extremely low miles" on an 1150 isn't necessarily a good thing imo. Don't apply too much premium there. Could still have much maintenance in store. Should have more than 45k just to demonstrate lack of build defects. Actual condition is more important than odo. Documented 50-75k from exp BMW rider might have new rotors, tires, batt, m cyl, clutch slave, fuel pump, hoses, cables, free of dry seals, ect.