ok well if it is placed in the manifold what would be the highest temp it could withstand
That is sort of a loaded question that would depend on several factors, one being engine timing.
Many claim that advanced timing lowers EGTs; but, that is not quite the case.
Advanced timing keeps the combustion heat inside the cylinder longer, allowing it to cool somewhat before it exits into the manifold, thus "fooling" the pyrometer into giving a reading that is somewhat lower than the actual EGT.
Retarded timing does the reverse and actually gives a more accurate indication, due to the heat getting into the manifold quicker.
The health of the oil and coolant systems play a big role in what is safe EGT.
A piston that has good clean cool oil being generously sprayed into it's bottom side, operating inside a cylinder that has a clean healthy water-jacket with clean fresh coolant being generously circulated around it, can live longer in higher temperatures than one that suffers from poor lubrication and questionable cooling.
To be absolutely safe, one should stay below the melting point of whatever aluminum alloy that his particular pistons are made of.