What you have to remember is that those engines are already very very strong. So adding more power is just a case of getting more air in and out (intake and exhuast) and turning up the boost. On an N/A car, like the Zed, they are already very well tuned to get the most power from it (pretty much). Increasing airflow doesnt make any big difference as the Zed has targets in its ECU for torque at a given rev/load and will tweak the mapping to get it to that number. By mapping it they can change that target and fiddle a bit, but you wont overcome the fact that the engine is already very heavily tuned for the state its in already.
Well those engines are built with boost in mind, 400hp seem to be the figure that the Z can run without touching the internals (whp?) so you dont' need to go touching the internals if you dont want to run crazy hp figures (like I do )
The manufactors build an engine to last for X ammount of miles so when you overboost an EVO or GTI etc you will kill of that life span, I'm not sure which of them are the 'safest' to boost up but when you look at HP per €/$/£ you always 'win' with a turbo...
A.
Personally I couldnt compare the GTI or EVO to the Z different class all together just by looks!