WDeranged
Have you installed latest patch, by chance? If so, you don't need to edit XNL-file in game's dir, there is an in-game option for that already. Changing "[...]\Divinity2_DKS\data\config.xml" won't affect anything on versions above hotfix one.

Just a fun observation: all ppl who has issues with GFX/fps here uses ATI. It could be fun if it wasn't so sad.