I've only used the same single ferro rod, that was the reason I started the post, to find out more.Which brands do you consider soft and which hard? Have you tried the UST and Coghlans? I use those the most.
I do have knowledge of metals, alloy's the purpose behind Alloy ratios for different purpose. So I understand the reasoning between the softer and harder options.
My curiosity initially came from something I had seen, that you have now answered. I seen various rods online (images/videos) that had a really short stroke at the tip with deeper wear than others. When I stumbled across the video I linked to I reckoned this must be the reason.
But have brought something else up...
I scrape the full length and have experienced the juddering in the past. But now I use a, wait for it... junior hacksaw blade section. Teeth side too.Because of this I have moved to making approximitely 1" long scrapes, always on the same area, no matter which ferro is used. Funny how I used to scrape the entire length of a 5"L x 1/2"dia ferro and now 1" of a 1/4" ferro is enough. With knowledge comes skill, with skill comes joy.
Looks like I'll be moving away from that then. I reckon I'll give the shorter strokes a go, I've never tried it.