"Hypereutectic pistons (which are also cast) were introduced over a decade ago for OEM engines that required something stronger than an ordinary cast piston. Hypereutectic alloys contain a much higher level of silicon (16.5 to 18 percent versus 8.5 to 10.5 percent in a typical cast piston alloy such as SAE 332 or F-132). Silicon increases hardness for reduced ring groove, pin boss and skirt wear. Hypereutectic alloys are slightly lighter (about 2 percent) than standard cast alloys, and can be machined somewhat thinner to reduce overall piston weight about 10 percent.
Hypereutectic alloys also handle heat better than standard cast alloys and undergo about 15 percent less expansion when the alloy gets hot because its silicon formulation rejects heat. Since hypereutectic pistons don't conduct heat they can be installed with somewhat tighter cylinder bore clearances to reduce ring flex and piston rock for improved sealing. Hypereutectic pistons that are made for performance applications may also receive a heat treatment to increase their strength; but how much is necessary is a subject of some debate. According to some sources, a "T6" heat treatment can increase strength up to 30 percent, but other engineers say this strength is not permanent: T6 is only stronger than T5 for the first 100 hours. A T5 heat treatment, on the other hand, gives a linear increase in strength over the life of the engine, which may be a better choice for many performance applications.
Many late model engines today come factory-equipped with hypereutectic pistons. In many instances, the OEM hypereutectic pistons can handle engine modifications that boost power up to 30 percent or more over stock. Aftermarket hypereutectic performance pistons are available for upgrading a wide variety of engines including SB/BB Chevys and Fords, as well as many late model engines and sport compact engines. Some racers are using hypereutectic pistons successfully as a lower-cost alternative to forged pistons on circle tracks and drag strips.
One manufacturer said hypereutectic pistons can usually handle up to 1.5 to 2 horsepower per cubic inch of engine displacement. Beyond 2 horsepower per cubic inch, they would recommend upgrading to forged pistons. The manufacturer also said its hypereutectic performance pistons may be able to handle up to 1,000 horsepower provided the fuel mixture and timing are correct so the engine doesn't go into detonation or preignition."
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10% less weight, 15% less expansion. Those aren't small numbers. Can't find anything that equates that to power production exactly, but both of those decrease engine wear, and thats completely ignoring all other benefits of weight reduction, tighter tolerances, and heat rejection. Like I said, with those benefits, for $20, I'm surprised cast is still around.
I don't know, I guess if going for absolute budget build, the $20 difference over cast could be seen as a waste.
Just kidding of course, but with a budget of $150, I see no reason hypers aren't the only choice. 
