In my opinion the V8 is the safer platform to modify. The 2.3L Ecoboost will probably be near the ragged edge at 400-450 RWHP, if this power level is achieved without significant internal upgrades.
This will depend on how well built the 2.3t is from the factory. It is certainly conceivable that big power can be gained from ecu,intake,exhaust upgrades. If the motor is as stout as say the 2.0t motors in say, an Evo, a bigger turbo+intercooler added to the 2.3t can lead to some pretty big power. The good thing about turbo motors is that they are generally designed to take a lot more stress than the average NA motor.