NZ Rail Maps: Optimising Gimp and using 4x4x4 grid for mosaics [4]

Last time I posted I wrote about my experiments rescaling layers in Gimp from 0.4 metres to 0.2 metres pixel spacing and 0.3 to 0.15 metres pixel spacing and seeing how these matched with the NZR station surveys.
I am still in two minds about whether to go with 0.2 metres from 0.4 metres source imagery because the 1:4300 layers in particular have to be scaled down to 70% of their original size, which is enough to lose quite a bit of sharpness. At 0.15 metres they would be about the same size, at 0.1333333333 metres (0.4/3) they need to be scaled up by 6%.
So at the moment I am redoing some of the Otago Central station survey mosaics with 0.4 metre base imagery scaled to 0.1333333333333 metres and then a layer that is 3×3 for Qgis that is 14400×21600 which is quite large but not too hard to load so we will have a go with that as well as continuing to experiment in the MSL coverage but that so far is generally 0.3 metres scaled to 0.15 metres so it does not have same challenges as 0.4 metre stuff.
But of course for the lower res corridor surveys and state highway surveys we can go at 0.3, 0.2 or whatever without too much resizing because it is a lower resolution so stations that come under those surveys aren’t such a challenge.