Late addition, just tested VIPS with:
https://test2.wikipedia.org/wiki/Special:VipsTest?file=Fern+Groombridge.JPG&...
and found the non-bilinear VIPS version with its loss of detail rather disappointing.
Bilinear scaling with sharpen 0.8 I find unacceptable, https://test2.wikipedia.org/wiki/Special:VipsTest?file=Fern+Groombridge.JPG&...
closest results I had with 0.5: https://test2.wikipedia.org/wiki/Special:VipsTest?file=Fern+Groombridge.JPG&...
... but imagemagick is definitely still best.
Is it possible to use VIPS only for oversized images?
Gregor