I have to disagree, I'm going to be getting a Z5 also and I'll be projecting from the shelf of my coffee table from about 6'8" (2.02m) away giving an image of around 60" (146cm) on a 65" screen. This is possible because of the Z5s short throw lens.
a 60" image is as big as I want to go as we only sit about 8.5 ft away. We have a 37" LCD for everyday use and I personally wouldn't want a bigger screen sat there all the time blocking my bay window. Much prefer being able to pull down the screen only when required for movies. I also wouldn't want to blow SD Freeview and Sky up to 60" all the time - would look terrible!!
Total cost for this including screen (manual) and cabling (10m hdmi) will be under £750. A 60" 720p plasma would cost about £3K so no comparison on price. 50" plasmas are about a grand now but I'd rather go for the extra size and only intend to use it at night for HD movies.
Anyway, back on topic

- you should get a 81" image from 2.5m.
For screens have a look here:
http://www.cvsmedia.co.uk/shop/index...19_259_253_273
They do some screens with long drop so you can get the image at eye level from your sofa. The one I'm planning to get is a 65" (61" viewable) projecta slimscreen which has a 90 cm drop. They do an 82" one (76" viewable) with a 77 cm drop.
If you get the Z5 let me know how you go on, just waiting for pay deal to be settled at work then I'm getting one.