Single data point here but I just switched from an NVIDIA GTX 960 (2015 card) to an AMD RX 570 (2017), both using open source drivers, and the performance improvement in Wayland/Sway is huge.
My understanding is that even 2015 is too new for nouveau to run with high performance due to something called reclocking, where the card starts up at a minimal clock rate and then it's up to the drivers to reconfigure it for running at the advertised clock.
My understanding is that even 2015 is too new for nouveau to run with high performance due to something called reclocking, where the card starts up at a minimal clock rate and then it's up to the drivers to reconfigure it for running at the advertised clock.