I think there are couple of things to ask yourself:

a) what kind of power delivery do you want
b) how much are you willing to spend

I think you will be able to get more bhp/£ from the zetec, but either way I reckon for the kind of power you seem to be describing (300+ bhp) you are going to be looking around £5k + for it to be built if you want it to be reliable.

Obviously the turbo that you choose will play a part in how much power you get and how it drives, ie smaller turbo for less power but more drivable, or big turbo for bigger power but possibly less drivable (will give you a kick in the back once it kicks in!)

What do you want from the enigne? something you are going to be using on a regular basis or something that you are mainly just gonna be taking out for a blast?