You are certainly not good to go.
In the first place they have given you a 8 Pin connector onboard, irrelevant of whether you are using the current from them or not, you really need to use all those pins since you will have absolutely no idea as to what plug takes current to which parts. When you supply any electrical component with less or excess of current you are bound to see a wear and tear in the equipment. I'd suggest using all 8 pins first.
Yes, the game is going to be heavy on the CPU, you might as well see you it that it is fully powered on or you might just end up with a blown capacitor.
Note to Samuelspark.......
He's not asking about his Temps..... read before you give advice. A totally unrelated answer to the question the OP poses.
Yeah, I'll go ahead and plug in the second four pin. I just wasn't sure if I should or not based on the fact that ASUS put a plastic removable cap over it.