So how does an ISO-threaded freewheel differ from an English-threaded one? The Sutherland's table perhaps implies that ISO has a thread pitch between those of English and Italian, which both otherwise have the same callout diameter and the same number of threads per inch.

I don't know about the rest of you, but my favorite freewheel size, 14-26, seems very hard to find these days, and 13-26 is not that much easier to find. With a 42T inner chainring (minimum size for a 144mm BCD, with the rare and expensive exception of a 41T ring), 24T gives me too high a bottom gear, and 28T doesn't get along with my SunTour Cyclone and Campagnolo NR and 980 derailleurs.