What configuration to choose for serious CG ?

I’ve been using Blender for 2 years now, and today I feel the need to work better on CG.
I’d say my level is intermediary for now, but my goal is to reach good photo-realism, which may be the most demanding style when it comes to CG, so that’s why I would need to upgrade my configuration sooner or later.

My actual configuration is the following : Windows 7 64 bits, AMD Athlon X4 760K at 4.2 Ghz, Sapphire ATI Radeon R7 260X at 2 Go, RAM 12 Go (Kingston Hyper Fury 4 Go + 8 Go) ; it’s what you would call a medium computer for Gaming.

So I would need clues about what configuration to chose when it comes to “heavy” CG work (for renders only, not animation), to speed up render time and overall software speed.

What would be good Graphic Cards or Processors for devoted CG work ? Some people recommended me Nvidia Quadros ; the most expensive is about 7000$, which is as gold or diamonds for me. I’m interested about the GTX 1080 at 8 Go, but it’s considered a GC for Gaming. Can someone explain me the difference between a “Gaming” card and more “Professional” cards I guess ?

I have less knowledge when it comes to Processors. What about the Intel Core i-7 ?

Overall, what would be reasonable “professionnal” materials to choose at the moment for CG, may it be economic or professionnal prices ?

PS : By the way, I need to render on CPU mode because of SSS in Cycles.