I'd start with the SSD. First, because you want one anyways. What I mean by that is before any other upgrade, you should have an SSD at this point in time(2016). That will help with load times, assuming you install your game on the SSD. If the occasional stutter in game is related to loading new resources, it'll also help there.
Meanwhile, take a look at benchmarks of the FX you are thinking about getting. A quick search shows me that a fast Phenom II is pretty much the same in gaming performance. That's a questionable 'upgrade' at best. In the Deus Ex game, AMD CPU performance is really all about clock speed. I'd try overclocking, a little at a time, your CPU to see if that helps. in my opinion that's about all you'll accomplish by getting the FX, acquire a higher clockspeed CPU.