It seems to me that the size of hole in the nozzle shouldn't matter in and of itself. If you program in the layer height and line width, then the same amount of plastic has to be extruded, no matter what size the hole is in the nozzle.
Of course I understand that, mechanically, the best results are got with the line width slightly larger than the nozzle size. We couldn't print a 0.3 mm line with a 0.6 mm nozzle, and trying to print a 1 mm line with a 0.4 mm nozzle probably wouldn't work well either. But in terms of what the actual G-code needs to do, the nozzle size doesn't seem to matter. After all, printers feed filament based on length/volume, so the size of the nozzle shouldn't impact the amount of plastic extruded.
What prompted this question: I want to switch from a 0.4 mm nozzle to a 0.8 mm nozzle, but I cannot find out how to change the nozzle size in Cura. There are many bug reports about the nozzle size setting disappearing or not displaying in Cura, and I think that's my problem. However, in the troubleshooting threads, many people claim that you can just change the line width and ignore the nozzle size completely and the result will be the same. In other words, if I want to switch from 0.4 nozzle and 0.48 line width, to 0.8 nozzle and 1 mm line width, I can just keep my slicer set to 0.4 nozzle size, but increase the line width to 1 mm, and if I physically install a 0.8 mm nozzle, it will do exactly the same thing. There are even Cura developers saying the nozzle size setting will be removed in a future version completely.
This may depend on the way individual slicers work. Has anyone tried switching between say 0.4 and 0.6 nozzle settings, while leaving the line width the same (say 0.8 mm line width for both), and see any differences in the G-code? I can't test this myself, because I can't change the nozzle size right now...