Depends on the resolution you are playing at, 720p it will be decent, but I suspect at 1080p it will slow to a crawl.
The bottleneck in gaming is always the GPU, HDD will only affect load times. A better GPU will give more performance than an SSD (though general system usage will be much better though). The next step up would be to a HD7850, or a GTX670 if you can afford the big jump.
I don't really see how that's possible unless as Manofchalk stated, you are only running at 720p. I had a 560ti and could run a couple settings on Ultra with all AA and AF filtering off at 1080p and I would estimate 40 to 45 FPS.