I have an Asus X750JB, a cheaper variant of the G750. Real solid build, the metal plating below the keyboard helps a lot in heat management. The processor is the same in the two models and it has 8 logical threads. You can't really strain it to 100% with normal use. The Nvidia 740M can handle most newer games on medium settings, so I'm sure the 8xx cards those come with will be up for pretty much anything. Be sure to get a heat dissipation pad to put it on though, it increases longevity a great deal.
Good place to look how individual components will fare:
http://www.notebookcheck.net/

They even have FPS averages on different settings in popular games at each article's bottom.