cpu bottleneck question

Will a C2D E6550 bottleneck a GTX 260 @ 1680 x 1050? Case in point: I tried overclocking my video card and got 0 more fps. I'm wondering if my CPU is to blame or at that resolution there is no gains from the card. 136 FPS no oc, 136 full overclock.

However the reason I'm asking because in the game I play Aion.. I get massive lag at raids in fortresses and I get under 15 fps and under 30 if I make everyone invisible but me.

Is my cpu to blame?

If you need my exact rig specs for reference, they are

E6550 @ 2.93 ghz
Gigabyte P35-DS3L
4 x 1gb gskill ddr2 pc6400
BFG GTX 260 stock/ 675:2304
Samsung 225BW @ 1680 x 1050

Task Manager will show CPU utilization.
If it is 100% and stays there, the CPU is a bottleneck.
You can get better monitoring results by using Performance Monitor to create a performance log that can be customized and replayed.

For a card like that, 1680x1050 is nothing, so in terms of gaming at that resolution, yes your CPU is why your FPS are not going higher with the video card overclock. Since I'm guessing that the resolution in question is the native, and thus highest, resolution of your monitor that upping the resolution is not an option. As such you take advantage of what you have and start turning on all the eye candy to improve appearance.