scaledTexture: Lower performance for some images and/or zoom levels,
Examples
Death Valley
This one does okay for a many zoom levels in the Demo with Triliniar. However, for scales 0.5 and larger, the FPS drops when panning and zooming. It's already better at 0.15 but still pretty visible in the FPS for me.
Nebula
https://stsci-opo.org/STScI-01GA6KKWG229B16K4Q38CH3BXS.png
This one is slow on all zoom levels in the GTK Demo for me. While it is much smaller than Death Valley. Even while not zooming or scrolling the FPS can go down to 3 FPS.
The latter sounds a bit like the texture is regenerated in each frame.
However, there is nothing special about this image. Just a colored square SVG with 14k x 14k resolution has the same problem: 14k.zip