The 4805 seems to have some minor flickering and sync issues on some models that are bugging people (according to AVS forums) though I did not see any when I demoed the one over at the mini-Mag at Best Buy. Tiger Direct right now has the 4805 at $900.00 with a $100.00 mail in rebate bringing it down to 800 bucks - great price on an excellent projector.
You really should not be sitting any closer than 2x screen WIDTH on these projectors for the best quality, though a little closer won't kill you, it'll just make resolution a little more noticable.
Even with a very high resolution projector, about the closest you would ever be comfortable sitting is about 1.3x screen width, and you would want a really good projector if you would be that close. So, at 12 feet you want about a 6 foot WIDE screen - 72" wide. A little more - like a 45" x 80" screen will give you a 92" diagonal which will blow you away from 12 feet back. Yes, you can go bigger, but you should then up your budget to allow a Panasonic AE700 or InFocus SP7205 at the very least...
Thought the Sanyo Z2 may be worth considering as well.