Upgrade Advice Please

[MSPV12]

Hi folks,

Just getting into CoD and wondered if anyone can advise me if it worth upgrading my pc at all?

I have the following;
Intel Core2 Quad Q8300 2.50GHz with 4G Ram, Win 7 and NVidea GeForce GTX 260 with 896mb GDDR3 Memory

My average fps on the blackrain (i think thats what its called) video track is 26, with high of 64 and low of 9. This is with all settings at medium, (except forest is Low), at 1600x900

I notice a better vid card is huge money. Is it worth getting another 260 to add to my existing card in SLi? Is my CPU good enough?

Hope this isn't too vague. I'm not particularly technical.

Thanks in advance.