Well I swapped my QNT chain at 1800 miles or so (it was covered in sand after a two tours in Suffolk) and fitted a new 2 and 2/3rds chain.
The old one is not worn out, showing much less tan 2/3% wear on a Park tools chain checker, (the 2/3% bar is nowhere near going into the link) neither the cassette onor the chainrings show any discernable wear.
After cleaning it and regreasing it in a chain bath it is now waiting for 3600 miles to come up to go back on the trike. I expect to use both chain lenghts at least twice and possible three times before I need to change chains, cassette and chainrings.