New processor or new mobo and processor and RAM?

[Scipio]

I've got a pretty dated rig (Socket 1155), with i5 dual core processor and 16 GB DDR3. I'm pretty happy with it, except for some current gen games wheeze the processor while running. I can get an i7 quad core processor for under $400.

[viper37]

the CPU will give you a boost for modern games that run on DirectX 12 or Vulkan.  It won't do much for DX9,10,11 games.  Check the games you want to play first before investing.

What is your processor exactly?  Most i5 are technically 4 cores, 2 real cores X 2 virtual ones (4x2 for i7).

Going from i5 4690k to i74790k gave me a small boost in performance in many games, but not that much.