I have not noticed any particular problems so far, apart from the fragmentation of the GH card
...
cannot seem to find any reference to "4nec4" on the website.

Yes that's correct. 4nec2 (for nec too...) does 'understand' both nec2
and nec4 in- and output-files.To switch from Nec2 to Nec4 use
'Settings-Nec engine-Nec4*.exe'.
However the interface between 4nec2 and Nec4*.exe is a bit more
primitive compared to the Nec2 interface. This because of the unability
of input-file redirection for the average Windows-based Nec4
compilations.

I tend to have a bias towards GNEC

Ah, no problem at all. Choose what you like best !

Thanks for the feedback,

Arie.,