Is a x4 955 overkill w/ a Nvidea 9600GT?

For gaming, assuming you are not running any CPU bound games (ie GTAIV, FSX,etc) then the Athlon II will be fine. If you run multi threaded programs (ie Photooshop CS5, Vagas,etc) then get the X4.

Yes--it is overkill. Basically any decent new processor is overkill for the 9600GT. If you are just upgrading the processor you are better off getting something cost effective---and not overpowering what your older system can really take advantage of. It is common for gaming computers to have graphics cards that are more expensive than the processor--processors do not bottleneck graphic cards as easily as one might think.

The x3 Rana line are a good value and highly recommended. A triple core athlon with a high clock speed will be just as good for gaming as a more expensive quad core phenom.

For gaming however, i would also look into boosting the GPU sometime soon--there have been some pretty decent shifts in GPU tech--you could get a big step up from the 9600GT in the low $100s.

I think it's not overkill.

Processor and VGA works differently. The faster the processor, the faster the loading times. But once it gets into displaying them, it's the work for VGA, not processor anymore. So no matter how fast a processor it's not an overkill for the VGA. Processor only 'process' the data (code, compiling, etc. code-related). The displaying frames per second will be VGA's doing.
So, X4 955 is not an overkill. It will help the loading times. Once it gets into play, it's VGA that plays the smoothness. The more better your VGA, the smoother it'd be.

So in terms, go for the X4 955. It will be significant difference between 2 & 4 cores in gaming. Especially for heavy games when there's a movie playing when game loading, like MW2.

Not entirely true. Loading times mainly depend on the HDD and than on the motherboard's chipset and than on the processor. The processor is the destination, not conveyor...
all the rest was valid reasoning...