PBTH contracts will yield the numbers. If your airline calculates 'cost index', then the variables of fuel cost and maintenance cost are integral to that calculation. The 'revenue' side of that calculation, e.g. the cost of a missed connection by the pax versus the increase in fuel burn/ maintenance cost by flying faster to make the connection, is a more complex variable. FLEX is also about maintaining engine EGT margin at high power, i.e. Take Off Thrust; however, the recent attempts (abandoned by most A340-300 operators?) at EGT margin retention on the CFM56 (the so called '-P' project), shows that you can get the EGT gauge to show a healthy margin against the limiting figure without getting a retainable increase in payload or improvement in fuel burn.