SentraSE-R experimented with different loads with engine off P&G, and if you don't do it right, almost no savings, at 70% load during accelerating, vs just leaving it in 5th gear at the same average speed his MPG was practically the same at 55mpg(32.5 mph). At 82% load 66 mpg, and 90% load 72 mpg.
Depends a lot on the car, only way to find out is to try yourself using others experience to save some time.
http://ecomodder.com/forum/showthrea...d-19594-2.html