If you have to choose I would send 1080i over 720p, there may be times it may be noticable, tho I agree on smaller sets its harder to discern.
With DirectTV-HD satellite I get HD channels in 1080i and the others in what I think is 720p, and there is no comparison. I will now only watch HD channels.. but I am using 60" Elite plasma.
BTW Tgrisham would your friend recommend calibrating the 151 elite plasma?