This is not true.
You should read Corky Bell's book "Maximum Boost." He goes into a good amount of detail about the differences between inertial and power loads, how they interact and about why the former is actually tougher on engines than the latter.
Some salient points from his book:
- inertial loads come about from RPM and the loads increase as the square of the RPM increase
- inertial loads are the worst of the two loads because they induce fatigue failure of components
- the tensile forces on the connecting rod at TDC are maximum on the exhaust stroke and load here increases as the square of RPM
- power loads are not "instantaneous" like inertial loads; power is a function of average pressure during the power stroke, not instant
- pressure under boost at 90o crank angle are 3-4 times that of a N/A engine but are still less than peak pressure and are thus not damaging
Get the book.
Small normally aspirated engines (if one can call the 4.6 "small") need to rev to move the air required to combust enough fuel to make power. It's why most small performance import engines need to turn 7000 or more RPM before they reach peak power. It's why F1 engines need to turn 19,000RPM to make their power.
RPM is more damaging to the engine than cylinder pressure resulting from forced induction. As an added feature, high RPM operation with mods (at least 2Vs) tends to fill the cylinder heads with oil unless drainback as been enhanced. This can lead to oil starvation if the pickup is exposed to air and a spun bearing.
As well, lets not forget having to control those valves at high RPM. Ever see Spintron footage of a valve operating at high RPM? Like:
YouTube - Valve Float
If seeing that doesn't make you nervous you're not human
I think the main reasons F/I engines come apart is thermal management and/or detonation from a bad tune resulting in the piston structural integrity failing. When that happens, the top of the rod come loose and becomes a battering ram. But it's not the outright power or cylinder pressure that's killing the engine, it's poor combustion and/or poor heat removal.
FRPP just introduced a 2.3L Whipple twin-screw blower for the 5.0L engine in the '11 GT (the "Coyote"). At just 7psi that combo produces 525HP and 470 ft-lbs of torque. And, if you can believe it, if the kit is installed by the Ford dealer, you get a 12-month/12,000 mile warranty.
And if you can live without the warranty you can get 624HP and 536 ft-lbs from just 9-psi.
Keep in mind that the Coyote uses powdered metal rods not so dissimilar from what's in our lowly 2V and it also uses similar brittle hypereutectic pistons. No forged goodness here and still the thing is capable of 525HP with a warranty.
There's no question that forged parts add a safety margin and strength and tolerance for less than ideal conditions.