Iron blocks are good up to 800-1000 teksid is like 1000+ area as far as what it will handle as a race prepped block.
A 5.4 iron block has close to 1 inch taller deck and that ectra inch of iron at the top of the blocknon each side is where most pf the added weight comes from. And the additional weight of the rods by a few ounces each.
Most pre 2002 5 4 motors came from the factory with forged cranks.We put a stock block stock forged crank in my buddys GT with forged pistons and rods for another $750.(Motor was free) the car easilly made 522/650 on 15 psi