If your games are playing well, there would seem to be no reason to upgrade.
Do not be concerned about vram. The amount you have will be appropriate to the graphics card.
For better gaming, I could certainly see how a cpu or a gpu upgrade could be better.
This is a perennial question.
Here is my stock approach to evaluating that:
Some games are graphics limited like fast action shooters.
Others are cpu core speed limited like strategy, sims, and mmo.
Multiplayer tends to like many threads.
You need to find out which.
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To help clarify your CPU/GPU options, run these two tests:
a) Run YOUR games, but lower your resolution and eye candy.
If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics configuration.
If your FPS stays the same, you are likely more cpu limited.
b) Limit your cpu, either by reducing the OC, or, in windows power management, limit the maximum cpu% to something like 70%.
Go to control panel/power options/change plan settings/change advanced power settings/processor power management/maximum processor state/
This will simulate what a lack of cpu power will do.
Conversely what a 30% improvement in core speed might do.
You should also experiment with removing one or more cores/threads. You can do this in the windows msconfig boot advanced options option.
You will need to reboot for the change to take effect. Set the number of threads to less than you have.
This will tell you how sensitive your games are to the benefits of many threads.
If you see little difference, your game does not need all the threads you have.
It is possible that both tests are positive, indicating that you have a well balanced system,
and both cpu and gpu need to be upgraded to get better gaming FPS.
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What is your motherboard?
What is your budget?
You will have options for a cpu upgrade, keeping your motherboard.
You can increase your core or thread count, and you can improve the performance per core.
A power supply capable of running a GTX570 can also handle a upgrade to a modern card as good as a GTX1080.