The SCT MAF is capable of supporting around 700rwhp. You wouldnt need the SCT MAF or the extender unless you are approaching the 500rwhp mark. After that you have a choice. But the SCT MAF or the Extender to prevent the Stock MAF from pegging.
I believe the stock MAF size is around 88-90mm. The SCT MAF is actually a stock sized meter, but the electronics itself are different to support the HP. There is no need to go to a larger sized MAF really