GTX980ti is the strongest of your candidates.
Here is a hierarchy list:
http://www.tomshardware.com/reviews/gpu-hierarchy,4388.html
That said, your FX processor may not be able to get what such a card is capable of.
For fast action shooters, you may be ok.
I'm not a fast action shooter sadly, and the problem is I don't have any of these Gpus and I don't want to buy one when I know that another can do better with my CPU. Anything else you can tell me that can apply to me situation?
for others like sims, mmo, and strategy games not likely.
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. 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 processors 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.