You can, and likely should, use the resource monitor to determine what your bottlenecks are.
If anything reaches 100%, or close to that usage, that component is a bottleneck for your desired usage.
So upgrading that component will increase your performance.
Something that is only reaching 60% utilization isn't likely a bottleneck.



The Intel processors are generally miles ahead of the AMD processors.

The current 8-core AMD processor is not even close to the current gaming 4-core or 6-core Intel processor.
But you can tell that by their relative costs.



The motherboard is going to determine (by its' socket type) which CPUs you can use.
It might limit your ram somewhat, to say 2-channel instead of 4-channel ram.
So motherboard/CPU are generally larger upgrades.

The other upgrades on a system are generally going to work in multiple systems.
So you can upgrade your gaming drive to an SSD.
Or add more system ram or a better video card.
If you upgrade to a new system down the road, you can add the SSD or powerful video card you get now.
Assuming you go for something other than ram/cpu.