I have 32 days left in which I can upgrade my current Video Cards from EVGA.  I currently have (2) 8800GT Superclocked cards in SLI , in an old xps 600, and due to bottlenecking of my old system, I haven't really seen then perform yet. I am just wondering what you guys think about me stepping up to a faster card. I am building my first pc in about 2 weeks, and it's a top notch gaming machine only. I will only be gaiming on it, and I run a 24" monitor. Once I get the new system set up, I am wondering if I should step up to a faster set of cards? I will be running these cards with an E8400 overclocked, on an EVGA 780i mobo. Share your thoughts. My total budget for this build with the price of the cards I currently have is around $2500. Feedback is welcome.

I would, for only paying the price difference it is a good opportunity to upgrade. But I would not get the 780i, DDR3 prices are coming down and the 790i has faster in SLI. If you really want DDr2 check out the EVGA 750i that OC's better than the 780i acording to :  
http://www.guru3d.com/article/mainboard/525/

Well the 9800GTX MSRP on eVGA's website is $350.  With the step-up program you cannot step up to any OC'd version of any card, just the base card.  The 8800GTS (G92) is also $350 on their site and is backordered.  This means the best card for you to go to is the 9800GTX at $350.
 
Say you spent $250 a piece on your 8800GTs, this means you will have to spend an additional $100/card to step up.

Dont they charge you the difference for what the 8800GTs are currently priced at and not what you paid for them?

They charge you the price of the card on their site plus shipping both ways minus the price you paid for the card.

Its funny that both the old generation (GTS512) costs the same as the newer one hmmmm OT just the same if you feel the need to use your stepup, go for the newer GTX, since the rumors are the G200 wont be out til late 3rdqtr at the earliest

 
 
Correct.  They use what you paid for the card, not what the card is currently selling for.