It would be difficult to know but I wonder what Lothian's
- Highest average speed block (right term?)
- Highest milage block
- Longest (time) block
- Overall highest daily mileage routes a vehicle might reasonably do
is, for double- and single-deckers. (I think "block" is the right term; for the working a vehicle does between leaving the garage and returning? As it might encompass multiple routes as well as dead running to/from the garage. I think "duty" is the equivalent term for the driver.)
I would guess a block on the X7 would be the highest average speed for single decks. For doubles probably the X6? If the blocks are quite short though then they may not be the highest mileage.
I guess highest daily mileage depends a lot on the overall block length.