Two potentially useful thoughts from a recent trip to the Antarctic on well-equipped Russian boat.
1. The Falklands are currently being surveyed using pairs of (interferential?) GPS's, accurate to a couple of centimetres.
2. The ship's crew used radar cross-schecked with the chart, not GPS, for going in and out of anchorages, day or night. They used only GPS for en route navigation and used the sextant once a month for practice.
I'm with FS: Option 4.
QDM