SSI EEB is the same size as EATX but some of the holes will not line up on the tray so you are kind of stuck getting a server case for that board because when you go to install your ram you will need the support only the outside edge screw holes line up.
Instead of going for the Quadro fx 1800, go and buy yourself the fx 3800 or even te 4800. There is a guy over in the classified section who was selling two of these cards that have no been used and still sealed in antistatic bags. I bought one for $850, and its a beast! you should try contacting him to see if its still available. you cant beat that price.
As for the case, Silverstone makes a few cases with that form factor.