It is pretty clear from Ryan’s test that stainless steel EMT of the similar wall thickness has less deflection under load. But it is crazy expensive.
Young’s Modulus be damned? No, but there is “steel” and then there’s STEEL. The stuff they use for EMT, which after all is designed to hold up wires rather than buildings, is the former variety.
“According to the World Steel Association, there are over 3,500 different grades of steel, encompassing unique physical, chemical, and environmental properties.” (Here, if you’re interested).
So, when you google Young’s Modulus for “Steel” vs “Stainless Steel” you are not likely to come away with any useful information. Of course, Google doesn’t tell you that 