Hmm. It still makes me suspicious about the monitor settings, but I'm not sure what it could be that Nouveau doesn't support or has alternative defaults.as long as I run GW1 in the background I can use the PC as normal even play games that were causing artifacts albeit at lower fps, this works on the newest drivers and the older ones, I have no idea whats going on, I can only assume that there is something that the drivers are doing to the graphic card but being that GW1 is so old the card is doing some form of throttling to accommodate the game.
There's the colour depth and temperature, DSC, HDR, overdrive... ?
I like KompuKare's theory about the clocks and power states too.