Do I need to upgrade my E6600?

You could always overclock it. I think ive seen people say that chip can OC easily to E8400 stock performance levels. However I wouldnt put much faith in that 680i board to give you a decent voltage level, drop/droop. Could turn into real hell.

+1
oc and see how much you can gain, but the e6600 shouldnt be to much of a bottleneck.

Also, i did not playing crysis, i found High appeared a little smoother and there were a few extra FPS in there... but nothing like i expected with a GTX 280 OC largely.

Don't use 3dmark vantage to test your cpu. Encode some x264. I would certainly not upgrade that cpu. Next stop should be nehalem. If there is a problem it is elsewhere. Run some standard crysis benchmarks and post your scores.

Yes, that does seem low. I can't speak for the CPU benchmarks as I never run them, but I get similar results for my 9600GT on the GPU benchmark at the same settings albeit at 1440x900. Are you running in DX9 or DX10? That makes around 5-8FPS difference in average framerates. It could be drivers too. Here is what I get (excuse the colours, there are too many data sets ):

Not all of them are directly comparable. Most were run on Vista x86 with 2GB RAM. 177.92 I believe was run with 4GB RAM (or 3.325 if you like) on Vista x86. 175.19 and 178.13 were run on Vista x64 with 4GB RAM. Additionally, the later drivers and also 175.19 were tested with more runs so are a little more accurate. As you can see though, the driver can make a good deal of difference, especially if it doesn't like your specific configuration.

Obviously if you are with a GTX280,you need something like E8400 or Q6600 onward to get the most out of your system.