If you will benefit from the monitors for productivity it may not be a bad idea to get the monitors now, even if you're not able to use them for gaming. You can still continue to game on your center monitor alone like you are now.
That said, as far as gaming is concerned Wijkert is right. I have a GTX780ti with an older i7 and 8GB of RAM and have to lower settings for certain games (Rome II/Attila) in order for them to play smoothly on all 3 monitors. You have to remember your GPU has to push 3x the pixels!
One last thing I would say, if you're going to invest into a more gaming-oriented monitor you probably want to make that one your center monitor. The side monitors tend to just cover your peripheral vision for the most part, so you'll spend the majority of your time facing the center unit. Especially on games like FPS where you simply move where you want to look, vs. an RTS game where the screen real-estate warrants moving your head around.
From a noob to a noob