Do you really need 1080i or 1080p or 1440p?
This study basically says that if you have 50” TV and you are watching it at about 9’ of distance then 720p has all the resolution human eye with 20⁄20 vision can ever see!
Currently we use 80X40 screen through our Panasonic projector PT-AX100U. Now that’s equal to almost 4 of your tiny 50” screens so certainly 720p won’t be enough at our current viewing distance of 10’ (our current screen size is limited because of wall size and I think the projector is perfectly capable of going up to 100” diagonal). Actually at that size looks like even 1080p won’t be enough. The 1080 runs out its steam at just 76” screen.
For now we will probably stick with our 720p projector though. The 1080p projectors are still super expensive right now($2500+)! Whoever said current HD technology is “enough”…