For emergency use, yes, I want the biggest one I can find. When you scrape a 1/2" firesteel with the toothed side of a cut-down hacksaw blade, you throw enough sparks to look like a fireworks display. You are able to start a fire much easier that way. The hacksaw blade is quite rough on your firesteel, but in an emergency you aren't terribly concerned about it lasting for thousands of lights. You'll probably only need a handful.

But for EDC, no, a large firesteel is not very convenient. I like your idea of the paracord holder. Not only is it a neat idea, but the result LOOKS cool too!