I think this is related: https://forums.opera.com/topic/17154/slow-scrolling-for-modal-windows

Not at all. It looks like all issues are solved in Opera Developer (v41) except in the Speed Dial and scrolling in modal windows. If I activate opera://flags/#enable-gpu-rasterization in Opera Dev, then it's silky smooth, but there is rendering actifacts.

Any plans to fix this performance issue? On my laptop, it's awful.

Same thing here. https://forums.opera.com/post/107415 Is there a specific setting affecting this?

I went back to version 39! Repaints are super fluid.

This affects Opera 40, Opera 39 was fine. When scrolling HTML modal windows, the scrolling is jerky and uses alot of CPU with < 20 FPS. This performance issue is also present in several settings pages:

Pages affected:
Quick access,
Bookmarks (seems better),
opera://extensions/,
Downloads,
opera://flags/

Pages not affected:
News,
Tabs,
History,
opera://settings/

I would say that the rendering method was changed?

Same thing for me, I use Opera for local development. My webserver is on a local VM, with local ip 10.0.6.10. Keeps asking, very annoying. It used to work fine in versions < 31.