Your cpu is not bad but by today's standards for gaming is a little lacking.
At what point going up the gpu ladder will that cpu be the bottleneck?
I dunno.......may depend on the game your running.
Tell us you have 1333 ram.
My Current Spec.
Mobo: Gigabyte GA-P55A-UD3
CPU: Intel Core i5 750 @2.67GHz
Graphic Card: NVIDIA GeForce GTX 470
Memory: Kingston DDR3 1GB * 4
OS: Windows 7 Professional 32 bit
And now I am thinking of upgrading my video card to GTX 700 series. So would the GPU be limited by my i5 or even the mobo ('cause it's a P55)?

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