I'll support those who say that your average speed over a longer trip will be less than when doing a short trip. An example from Newfoundland.
People from Corner Brook take 8 hours to drive to St. John's, Newfoundland at legal speeds. Likewise to drive to Port aux Basques at legal speeds from Corner Brook should take you 2 1/2 to 2 hours 45 minutes.
Yet the people who live in Port aux Basques plan on spending 12 hours to drive from there to St. John's. Or, they wisely plan on some longer stops on that longer trip.
If you've got pets, you will need to include things they enjoy and need in your stops.
:C