In regards to the question of whether or not upgraded rods and pistons are necessary for the 3.5L Ecoboost, here are a couple of photos of an engine that was sent to us for upgrading after suffering a failure. This was a rather high output engine with tune, turbos, etc. As the pictures show, there is a power limit to what the stock parts will handle before failure.
From examining the pistons, rings and bearings there are no signs of this failure being related to detonation or fuel. At power levels above 400WHP you start to get into a territory where the parts are near their outer limits, Beyond 450WHP you get into the territory where it's just a matter of when, not if, the stock rods and pistons will have a failure, because of this a piston and rod upgrade become practically a necessity in order to avoid eventual catastrophic engine failure. Again, while you could probably get away with running the stock bottom end near the 450WHP level, it's only a matter of time before the parts will catastrophically fail.
