There is a company that specialises in tuning the Powerstroke diesels with bigger turbos, intercoolers etc, ( I cant remember the name it is in one of those 5.0L and fast Ford mags I have from the US) but if you slap a chip onto a normal Diesel, you will get anything from 25-35% extra power and torque, and thats even before you go messing around with bigger turbos/intercoolers.
I know cause in Europe there is a power struggle between petrol and diesel. Good vs. evil.