Do any people have real world MPG figures for propane and  water and NOS injection systems?  

Out of the three, propane will show the largest fuel mileage gains. Water/methanol injection supposedly helps a little bit, but is mainly used for EGT reduction. NOS is used for hp gains only and shouldn't be used for more than 15 seconds at a time (per nitrous oxide systems). The only "real world" number I know of is the guy running CNG (compressed natural gas) in his Duramax in the Diesel Power Challenge in this month's issue. If I remember right, he was in the 36-37 mpg range in the fuel mileage test. He had reported getting near 50mpg during his testing. He was getting his CNG for about $0.80 a gallon. . I just paid $2.59 a gallon for propane to heat my house this winter.