Fuel less than planned is often accounted for by shorter than planned SID's & STARS + short cuts enroute. On a few trips, I have flown optimum uninterupted climb, CRZ at optimum, idle descent to straight in approach, spool up <1500'. Flight time was exact the plan to the minute. Sector flight time +/-1.45. Thus about 1.00 in CRZ. Taxi time at each end insignificant. The taxi out fuel was less than allowed and thus the taxi in fuel was already in the numbers. The fuel burnt was exactly the non-winglet plan. Thus no savings for the winglets.
Any other sector fuel savings I have made could be accounted for by shorter flight times. They balanced. The inflight winglet CRZ F.F. seems the same, within gauge error.
I assume that the long-haul heavies show some savings, otherwise what's the point, but for us.....? Hence my thoughts about takeoff performance.