Indeed. Bristol Bath Road long had just one King allocated, for years 6000 King George V himself, and it did used to take the Friday afternoon Bristolian up to Paddington, coming back certainly in summer on an overnight service which on Fridays were substantially reinforced with extra coaches. Rest of the week it had various diagrams as well. You don't see it often in photos of course but the several overnight West of England services with all the mail and newspapers etc as well as passenger coaches were all regular King work as well, they were very good at blasting heavy loads away from all the intermediate stops these trains made.And yet the operating dept treated them differently. Taunton may be able to confirm, but I believe The Bristolian in some of the 1950s timetables was diagrammed for a Castle on most weekdays, when it was seven coaches, but on a Friday it was eight coaches, and King diagram.
I can just remember the last of them, probably summer 1962. Not many but maybe one a day by then. From the footbridge west of Taunton you could spot a King half a mile back up the line in the station platform by the plate across in front of the bogie wheels. When they set off the exhaust was far heavier than a Castle, it's a wonder they didn't blast the paving slabs of the bridge up in the air. Although never allocated there, Taunton shed as the halfway-point had more than their expected share of turns on them as many WofE expresses were remanned there; Laira or Old Oak crews would turn round there to get home within the day, and so Taunton did a lot of express work to these two places. Drivers enjoyed them, fireman found them a notable challenge over a Castle. I don't think they got paid any more.