It would be interesting to know what the actual fuel burn and trip time would have been on the guardsvan. I have seen elsewhere that scheduled time for the flight even increased from the sixties to the present day. The total fuel loaded of around 6000kg on the turboprop seems remarkably similar, although the trident 3 looks eye wateringly high.
However the devil is in the detail. These days we rarely have a standard fuel. The last time I can remember was nearly ten years ago with a milk run route where we would load wings full fly an hour and then fly back without needing to fuel.
These days we take as close to flight plan fuel as conditions allow. Final reserve has been reduced from 1200kg to at times less than 800kg and single engine taxi, avoiding use of the APU, continuous descents etc. while individually quite small all add up to a meaningful amount.
The difference an individual captain can make, adds up easily into the mid ten of thousands per year just on fuel alone. Airlines seem very enthusiastic about buying new fuel efficient aircraft and quite rightly so. However saving on pilot's salaries is much easier to measure than the additional cost if you have demotivated pilots.