Many games are primarily single threaded.
Be careful how you interpret task manager cpu utilizations.
Windows will spread the activity of a single thread over all available threads.
So, if you had a game that was single threaded and cpu bound, it would show up on a quad core processor as 25%
utilization across all 4 threads.
leading you to think your bottleneck was elsewhere.
It turns our that few games can usefully use more than 2-3 threads.
How can you tell how well threaded your games or apps are?
One way is to disable one thread and see how you do.
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, it tells you that you will not benefit from more cores.
Likely, a better clock rate will be more important.
To help clarify your CPU/GPU options, run this test:
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.