For typical CPU intensive games like FSX, your CPU is very likely the bottleneck.
However, for typical GPU intensive games, it probably does not. Take BF3 as an example (which also works out the CPU), your Phenom II X4 840 does not appear to be a bottleneck. The CPU usage will be higher when compared to an i7 2500K. But it does not bottleneck when paired with a GTX580 (which is in the same performance category as your HD6950) at your resolution of 1920x1080 according to the review below.
The sure way to determine whether or not your CPU bottlenecks your graphics card at your resolution for a particular game is to plot a graph of game framerate (fps) vs CPU frequency (Ghz). See graph below for a hypothetical example.
Basically, the slope indicates the amount of CPU bottleneck. If the slope is steep, the BN is large. If the curve levels off, the BN is very small.
Edited by windfire - 3/4/12 at 11:11pm