Spot on 212 man, can't beat what is actually happening airborne.
If your really tight on planning it can be an advantage having some figures up front, but if your that tight you probably want the worlds most accurate wind forecasts too...
Obviously the actual figures depend on the model, the engine installation (and their condition) and the cruise power settings. Its a snack to take some notes in the one/s you fly at different levels, work out the DA's and the corresponding burn at the time and you'll get pretty good data to work with.