Since you are upgrading to play witcher which is a single player game that doesn't have the variable of having to deal with multi-player games that rely on servers etc as well. Yes it will be a big difference. Especially when you can run games at higher settings while getting same or better fps then you are getting currently on your set up. Eso will also look and run better. But like the post above. Even if you have the best set up possible. If the game devs don't have a stable game as well as server,your gonna encounter lag etc. Also, since you are jumping up to a gtx 900 series from the 600. Make sure your motherboard and psu can support that card as well as fit in your tower. Since idk what else is in your pc set up you might wanna make sure your cpu meets the requirements for witcher3. I think minimum cpu requirement for witcher was at least i5 and up. I could be wrong there.