To be honest i can't really say how the worst and the best aircraft factor against each other, we have over 50 737s right now, mixed between 700s and 800s, aged between 14 years old and delivered last week. With engines mixed around the whole fleet, both -7B and BE variants. So there are bound to be some differences, however they are taken care of at the planning stage and the difference between planned fuel burn and real fuel burn is negligible.
I can't comment on our airbus fleets (yet) as i do not fly them, however from what i hear it is the same there. The flight planning system (LIDO) together with up to date forecasted winds and performance data is incredibly accurate.
Last edited by Denti; 14th September 2013 at 13:02.