The crash behaviour seems to depend on the drivers used.
18.4.1 -> 18.6.1 (inclusive) result in a GPU reset (both monitors die, system recovers to a 'Unreal process has stopped working" dialogue).
18.7.1 causes a silent crash where the application simply closes with no error message and no driver reset.
These crashes occur reliably within half an hour of play in the actual game-world (not the menus!!!).
18.3.3 has occasional crashes (in the first variety - gpu reset and monitor losing signal before recovery) but much less often than later drivers. They can be eliminated entirely **but only in 18.3.3** by disabling TDR detection in the Windows Registry. Doing this in later driver versions reduces but DOES NOT eliminate the crashing.
DxDiag attached for reference, though everything is fine here