Same here, but what i can add is - i just reinstalled Win10 x86_64 and 2 days ago there were no input lag. So something changed in this 2 days (like Win update released?). BTW, do all of whom have this issue use Win10 or any other OSes are vulnerable too?
Ok, what i found out is that if you run it with administrator rights, there will be no input lag. But setting Run with admin rights flag in Compatibility tab for TwoWorlds.exe and starting it through GOG Galaxy isn't the case. You need to start this exact executable. The only user experience improvement i see is to create a shortcut for it to place on desktop or anywhere you prefer.
Thanks, I guess it does work better when launching the exe in admin mode. I have Win10 Pro x64 version 1607.