Actually, an SSD contributes very little to gaming. By far, you will see a bigger jump in gaming performance with a new video card. I'd recommend a GTX 660Ti, instead of the regular 660. That being said, your video card may be good enough to play games now, and if it does, please.....spend the money on an SSD. Everything will benefit from an SSD.
I would get a good SSD first, and then save up and get a video card later on.