Help - how much does positioning spoil picture quality?

[pgd]

I need to get a new projector, quick, and have been considering budget DLPs like the Infocus X10 and Optima HD800X. I read that both these projectors have sizable positioning offsets. My room's an odd shape - it's a trapezium when viewed from the side - so am worried that whatever I go for will mean that I'm getting far less on screen than comes through the lens.

The back wall is 7-8ft tall. The front wall, about 5-6m (17+ft) away is around twice the height of the back wall. To date, my (recently dead) Panasonic AE100 has been mounted on a shelf (so not inverted) @ the top of the backwall and managed to throw a nice 3m (10ft) wide image (with 16-9 aspect ratio). So, the projector's positioned @ a height which is above the bottom, and below the top, of the projected image. I'm guessing that continuing to mount a new projector @ this or a similar position would significantly undermine picture quality? If this is so, would it be enough to make me forget about paying the extra for something like an Optoma HD800X and settle for something like a Sanyo Z5? Given the funny room and poritioning constrsaints, are there better suited projectors out there?

Thanks,

PGD