The 760 is a good GPU unfortunately that CPU is a bottleneck. I had the AMD phenom X4 840 before I upgraded to my current CPU (AMD FX 8320). Running my current GTX 660 I was surprised by the improvement in gaming performance over the old CPU which to me was plenty fast under Windows, browsing, etc.
I never understood why some have a disdain for AMD CPUs, I have had nothing but a positive experience of them since I've started building my own computers 15 years ago. For me they make solid reliable products at a good price that suits my personal needs well.
Each to their own I guess. Back on topic I'd suggest a CPU upgrade if possible as nothing really uses 16GB of RAM yet gaming wise except a handful of games such as Battlefield. Many games are still written in 32 bit code.
What temps are you getting with the current CPU, I only lagged on games such as Sleeping Dogs and Mafia 2 when I had my Phenom when pushing the settings too high.