Yeah, I'm planning too. I just measured my case. It's 6 1/2 inches wide and it is longer than 10 inches long. So would a 8800GTS fit? Yeah I got around $500 to blow off, so a 8800GTS price is fine.
Is that your case that is 10in or the inside? I have the Evga 8800GT and the card is 9in so if the area inside where the card is going is more than that then you are fine.