To be honest, your PC specs are very much top of the line right now in regards to videogame performance. There are few games the i7 3770 in combination with a GTX 760 can't run on maximum graphics or even for the most powerhungry engines at least on high settings.
If you're looking forward to Inquisition as a reference point, I'd say no need to upgrade at all.
What I do think might interfere with your overall performance for demanding games is if you have an ITX/µATX cube PC. The components themselves are perfectly fine and even better than what I have (and I can run Bf4 on high settings with the odd ultra thrown inbetween and comfortable sit atop the magic 60 fps threshold), but if you do indeed have a small cube PC, it would mean you have very bad airflow, which in turn means that as soon as your components start working for real, say trying to render a demanding game like Inquisition might be, they will start to grow hot which, obviously depending on your thermal solutions, might cause your components to not hit their maximum performance or throttle down when they reach their thermal limits.
That might cause performance drops during prolonged gaming sessions.
So if you really want to upgrade something, I'd say go grab any decent midi-tower case, maybe grab an additional fan and install it in your case. That can be as cheap as fifty bucks and really help with cooling your components.
IF you have a cube PC and you frequently hit the thermal limits of your hardware only of course. Otherwise you are set up pretty nicely.