I have a 1988 5.7L 260hp Mercruiser with 800 engine hours which is generally well maintained and running well. Given the engine's age, would a new 5.7L (350 MAG MPI) have a lot more "real" horsepower? Although everybody talks about the new efi engines getting "better" fuel economy, what kind of real world fuel economy improvement could I expect (1%? 10%?, ...). Thanks