There will be a slight bottleneck, depending on how far that 860 is OCed, but the bottleneck won't be big enough to justify spending so much money on changing mobo and CPU.
You can try and buy mostly CPU optimized games in order to avoid the bottleneck
It's not that the CPU is slow, it's actually crazy fast.
Just the game devs don't care about optimizing their code. As a programmer myself, I am disgusted with modern games