They already run at around 20 psi. That's a lot for any engine. Ford is not known to over build an engine to handle a bunch of extra power, i have seen some of the older mustang engines split in half at around 500, that's not very much imo.
Granted the engines are turbo'd from the factory they are stronger yes. But to handle 300hp at the wheels for the lifetime of the car m sure it would shorten the life span. Speaking of strength has any one ever come across a tear down of an ecoboost? I would be curious to know rod size, main bolt numbers etc.