I've had another look at the lecture notes and found some information about weight and range. Obviously a crucially important topic.
Yes David, that's the info your father would have used. Speeds were even slower than I thought but were seldom important, rather maximum endurance to loiter on convoy escort, opening up only when a target was detected.
One of his major responsibilities as f/eng, in between monitoring pressures and temperatures and adjusting mixtures for each power setting, would have been keeping a meticulous log of fuel consumption against time. The Sunderland had up to 10 fuel tanks which would be emptied in a prescribed order or perhaps transferred one to another using crossfeed connections. As each tank emptied, its capacity against time gave the fuel consumption which could be compared with the flight manual figures to reveal any inconsistency. This info would be constantly passed to pilot and navigator.
Of course there were no flowmeters to measure consumption of each individual engine and tank gauges were notoriously inaccurate. Some crews even ran each tank until the engine spluttered, so ensuring they took the last drop.
As regards overland flight, there were several instances of damaged aircraft alighting on land so it wasn't a problem, and a lightly loaded Sunderland could maintain height on three engines anyway. The Pembroke Dock aircraft had only to head west along Milford Haven and out into the Celtic Sea, towards the Western Approaches or the Bay of Biscay. The other big base, Castle Archdale on Lough Erne in Northern Ireland, had a short corridor across neutral Eire to avoid the long flight around Donegal – but in practice, I was told, they came and went via the most convenient routes.
Whichever way you look at it, your father and his colleagues did a fine job!