I have always been a fan of small, light cars with small capacity revvy engines. I currently run a Cinquecento Sporting. Old 1108cc engine, small light car, rev the nuts off it and it can emabrase most of the big German cars that think they can cut me up at roundabouts
Which is why I am not too bothered about a huge engine, I know what a small engine is capable of.
So if the smaller Zetec engines are all part of the same family then I can seriously think about using one, if the weight reduction is noticeable. If there is only a kg or two in it then I may as well stick with a larger Zetec.