It depends on the game, in synthetic benchmarks FX-6300 will certainly look bad compared to 2500k and AMD is failing in single threaded performance from a long time but in gaming it depends on whether a game is being CPU bound or GPU bound. Anyway I have no personal experience with FX-6300 so my opinion was based on these charts (they look far away but fps difference is small).
Those benchmarks look heavily GPU bound to me. Look how tight those scores are. Witcher 3 will be much more CPU oriented than any of those games, which are quite old at this point.


