Probably a lot less than you might think. Always remember macrumors is not a batch of 'normal' customers. Most people got an iPhone because they liked it, not because they had investigated a 'sweet spot' size beforehand and it just happened to be the size of an iPhone. I, like many others, happily had a 3.5" iPhone, but things move on, things change. I'm happy with a plus now. But who's to say in a few years I'll want something smaller again, or bigger still? Things. Change.