If you're getting a full warranty, I'd buy the 9000. It's a better projector than the 7800. My questions to them would be 1) Are they going to warranty the bulb? If not, will they put a new one in for you? 2) The fact that the 9000 was calibrated by a pro is great, but if you buy it, it would...
If your "very good deal" means buying a used projector, I would not do it. Much too risky. What are you confused about? Is your throw distance still 12' and screen size still 100" diagonal? I recommend you do the following:
1) Decide on 3D, yes or no
2) Decide on LCD, DLP or LCos
3) Max. budget...