Maybe you'll like to see performance with the linux-libre project from the FSFLA, they take the Linux kernel and try to strip all non-free parts.

AFAIK, the latest is: 5.2.

Jason Self maintains a deb repository: https://jxself.org/linux-libre/

Cheers!

Hmm...I could try that. I thought it wouldn't make a difference since Debian disables all of the non-free stuff from the kernel? But the latest version might have some improvements anyway.

If the performance is that bad, then maybe it's because the card needs proprietary blobs to have working 3D acceleration (although i doubt it as the rest of the Kepler 7xx cards listed here are marked as working). You should install the mesa-utils package from Debian's main repo and the run either glxinfo or glxheads and make sure it's not the kernel using software rendering (llvmpipe) in which case there's not much you can do. Also, i don't see how upgrading the kernel is going to do that much of a difference, you're on 4.19 anyway which is the latest LTS release.

AFAIK, even this card is listed here and proved to be working properly, I still get an error message about nouveau, see below kernel: nouveau 0000:01:00.0: bus: MMIO write of 0000001f FAULT at 6013d4 [ IBUS ] and those hidden problems has caused several crashes and errors inside my plasma DE...