The GPU will help your graphics in gaming, but the e5700 might limit it a bit. Hard to say for sure, but it's always good to have a better GPU, when gaming. Even the AMD 7850 would be a bit better than the GTX 660, but that is up to you to decide. Just remember that with a better GPU your going to be pulling in more power from the PSU and that might create issues with it. I would recommend upgrading the PSU and then upgrading the GPU.