Ledco
I believe that most saw blades that don't have carbide tips were run in the low 50s Rc. If they were run higher, they tended to chip or crack. The low 50s is a little soft for a knife, though it would be tough to drill with a HSS drill bit, I guess. If the blade got very hot when you cut/ground it out, it could be even softer. With that said, I once heard of a man sharpening a sardine can lid to a shaving edge to prove that inferior metal would still get scary sharp. I learned to sharpen knives on those old Pakistan lockbacks when I was around 12. I could get a scary sharp edge on them, which goes to show that even inferior steel will get sharp. It just won't stay that way.
Todd
Edited to add: I'll defer to Don on the hardness of the old blades. His reply came up while I was typing mine.