Very difficult to come up with a figure, and your examples are 'standard' fuel loads which I guess have long since disappeared in the days of shrieking accountants. At a guess, a 737-7 (Vanguard pax load) would PROBABLY load around 6-6.2 for a CAVOK LHR (given expected 21st Century delays), but that is conjecture. Perhaps a nice Nigel AB driver could cast a figure? Whether 6.2 for CAVOK would result in a 'coffee no biscuits chat' with one of the suits I have no idea since, of course, we have the 'no diversion fuel needed at LHR' modern age
