Video Card Advice

[NL__Fool]

I'm in the market for a new videocard. My current one is a little old and I would like to upgrade it.

As I understand it, I can have the best video card on the market today but it's no good to me if my computer can't keep up with it as it will only run as fast as my CPU. It will bottleneck somewhere along the way If I have an older CPU
Is this correct?

That being said I really don't want to shell out $600 for a Nvidia Gforce 8800 GT if I am only going to see a 5% difference between it and a $250 video card because of the speed of my CPU. On the other hand, if there is going to be a substantial difference $600 isn't out of the question.

Is there a way to calculate the performance increase? What would you guys recommend?

I currently am running an Intel P4 3.0 GHz cpu with hyper threading technology, & 2 Gigs of ram,

I purchased this back in May 2005.

My video card is a Nvidia gforce 6800 GT

How far should I upgrade my Video card before the price/performace ration becomes to expensive?