Probe should always be pre-turbo, either in the manifold or up-pipes. Never install the probe after the turbo in the downpipe, unless you just like to waste money.
As for 100 hp, EGT's can vary quite a bit depending on where you live (altitude) and which brand chip or tuner you purchase.
Safest "max sustained" EGT's is 1250 degrees (pre-turbo). But as was posted earlier, best rule of thumb to try and keep it at 1200 or less sustained. You can go over 1250 in short bursts (such as drag racing), but that's about it.
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