Hyperutectic is a term that denotes a high silicon content cast aluminum alloy. A Hyperutectic piston is "technically" cast, but has more resiliency than a typical cast piston. The thermal expansion is well controlled and they are lighter than a typical out of the box forged piston.
As Andre said, Hyperutectic are not forgiving with detonation, at their core, they are still cast, so detonation can cause them to fracture and crack. Forged aluminum while being more dense (and more heavy) is also more malleable, which means the piston can handle deformation without fracturing. That is not to say a Forged piston won't fracture, they sure will! But they are more forgiving in boosted and nitrous fed applications where there is the possibility of detonation.
The Fractured Cap Powdered Metal rod technology is nothing new. Basically what they do is they take a measured amount of powder that meets the specification for the material properties and it is forged under pressure and heat in a mold. The rod comes out of the mold with a very consistent finish and a very close weight tolerance. The rod is then finish machined, the rod and crank journal areas are finished and the finished rod is put onto a machine that "cracks" the cap off the bottom of the rod rather than cutting the cap off. This ensures that the cap will always be 100% aligned because the fracture is unique to each rod/cap.
Steel Forged cranks are old school time tested tech. Forged Steel is dense, strong and somewhat malleable before fracturing occurs. It's the strongest crank you are going to see in a factory engine, unless that engine is some high end, hand built exotic that is running a "Forged Billet" crank.
Here is an example of a Forged Steel modern Hemi Crank. The crank pictured is from a 6.1 Hemi, note the wide "parting line" on the ends of the counterweights. Cast Crank's will have a very narrow, very sharp parting line.
To put things into perspective.. Here is an excerp of the materials in the new ZL1 Camaro LSA.
Components and design elements that contribute to the LSA’s performance include:
■Balanced, lightweight reciprocating assembly
Nestled inside the LSA’s deep-skirted cylinder block is a forged steel crankshaft
that delivers a 3.62-inch (92 mm) stroke. It features an eight-bolt flange – the outer face of the crankshaft on which the flywheel is mounted – that provides enhanced clamping strength. Other non-supercharged GM 6.2L engines have a six-bolt flange. A torsional damper mounted to the front of the crankshaft features a keyway and friction washer, which is designed to support the engine’s high loads.
Connected to the crankshaft is a set of lightweight powder-metal connecting rods
and hypereutectic pistons, which, when combined with the cylinder heads, delivers a 9.1:1 compression ratio. The alloy of the pistons was selected for its strength and heat resistance properties, while the cast design
provides inherent quieting advantages over other piston materials, such as forged aluminum."
Source- Camaro Zl1 Exhaust | RoadTest TV