There is no such thing as "bottlenecking"
If, by that, you mean that upgrading a cpu or graphics card can
somehow lower your performance or FPS.
A better term might be limiting factor.
That is where adding more cpu or gpu becomes increasingly
It depends on the game.
Some are cpu limited and some are graphics limited.
If you play multiplayer games with many participants, your limitation of 4 threads will come into play.
Another possibility is that with 8gb you have insufficient ram.
A hard page fault will look like a cpu delay to an app.
Look at task manager memory tab for hard faults per second.
If you see anything over zero, you can use more ram.
It is hard to run anything at a constant 100% usage on all 4 threads.